diff --git a/README.md b/README.md
index 294c8b6..01893da 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ This module provides an easy way to build such tree and to add it to a page as a
 
 ## Requirements
 
-* SilverStripe 5.x
+* SilverStripe 6.x
 * (dnadesign/silvertsripe-elemental)[https://github.com/dnadesign/silverstripe-elemental]
 
 ## Screenshots
diff --git a/composer.json b/composer.json
index bec508f..456cf72 100644
--- a/composer.json
+++ b/composer.json
@@ -17,9 +17,9 @@
   "minimum-stability": "dev",
   "prefer-stable": true,
   "require": {
-    "dnadesign/silverstripe-elemental": "^5",
-    "silvershop/silverstripe-hasonefield": "^4",
-    "unclecheese/display-logic": "^3"
+    "dnadesign/silverstripe-elemental": "^6",
+    "silvershop/silverstripe-hasonefield": "^5",
+    "unclecheese/display-logic": "^4"
   },
   "config": {
     "allow-plugins": {
diff --git a/src/Extensions/ElementDecisionTreeController.php b/src/Extensions/ElementDecisionTreeController.php
index 4e4e4eb..bbffce7 100644
--- a/src/Extensions/ElementDecisionTreeController.php
+++ b/src/Extensions/ElementDecisionTreeController.php
@@ -2,34 +2,33 @@
 
 namespace DNADesign\SilverStripeElementalDecisionTree\Extensions;
 
+use DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeAnswer;
+use DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeStep;
 use SilverStripe\Control\Controller;
-use SilverStripe\View\ArrayData;
-use SilverStripe\View\Requirements;
 use SilverStripe\Core\Extension;
-use DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeStep;
-use DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeAnswer;
+use SilverStripe\Model\ArrayData;
+use SilverStripe\ORM\FieldType\DBHTMLText;
+use SilverStripe\View\Requirements;
 
 class ElementDecisionTreeController extends Extension
 {
-
-    private static $allowed_actions = [
-        'getNextStepForAnswer'
+    private static array $allowed_actions = [
+        'getNextStepForAnswer',
     ];
 
-    public function onAfterInit()
+    public function onAfterInit(): void
     {
         Requirements::javascript('dnadesign/silverstripe-elemental-decisiontree:javascript/decision-tree.src.js');
     }
 
     /**
-    * Return the HTMl for the next step to be displayed
-    * as well as the updated URL which includes the ids of the answers
-    * leading to this next step to be returned
-    *
-    * @param stepanswerid (POST)
-    * @return json
-    */
-    public function getNextStepForAnswer()
+     * Return the HTMl for the next step to be displayed
+     * as well as the updated URL which includes the ids of the answers
+     * leading to this next step to be returned.
+     *
+     * @param stepanswerid (POST)
+     */
+    public function getNextStepForAnswer(): null|bool|string|DBHTMLText
     {
         $answerID = $this->owner->getRequest()->postVar('stepanswerid');
 
@@ -41,7 +40,7 @@ public function getNextStepForAnswer()
 
         if (!$answer || !$answer->exists()) {
             return $this->owner->httpError(
-                404, 
+                404,
                 $this->renderError('An error has occurred, please reload the page and try again!')
             );
         }
@@ -50,26 +49,27 @@ public function getNextStepForAnswer()
 
         if (!$nextStep || !$nextStep->exists()) {
             return $this->owner->httpError(
-                404, 
+                404,
                 $this->renderError('An error has occurred, please reload the page and try again!')
             );
         }
 
         $html = $this->owner->customise(new ArrayData([
             'Step' => $nextStep,
-            'Controller' => $this->owner
+            'Controller' => $this->owner,
         ]))->renderWith('DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeStep');
 
         $pathway = $nextStep->getAnswerPathway();
 
         $nextURL = Controller::join_links(
-            $this->owner->AbsoluteLink(), '?decisionpathway='.implode(',', $pathway)
+            $this->owner->AbsoluteLink(),
+            '?decisionpathway=' . implode(',', $pathway)
         );
 
         if ($this->owner->getRequest()->isAjax()) {
             $data = [
                 'html' => $html->forTemplate(),
-                'nexturl' => $nextURL
+                'nexturl' => $nextURL,
             ];
 
             return json_encode($data);
@@ -79,12 +79,10 @@ public function getNextStepForAnswer()
     }
 
     /**
-    * Returns an array of DecisionStepID from the URL param
-    * in order to display the same question when we reload the page
-    *
-    * @return Array
-    */
-    public function getInitialPathway()
+     * Returns an array of DecisionStepID from the URL param
+     * in order to display the same question when we reload the page.
+     */
+    public function getInitialPathway(): ?array
     {
         $ids = $this->owner->getRequest()->getVar('decisionpathway');
 
@@ -96,12 +94,12 @@ public function getInitialPathway()
     }
 
     /**
-    * Check if an answer should be selected by default
-    * ie. The question depending on it is displayed
-    *
-    * @return Boolean
-    */
-    public function getIsAnswerSelected($answerID)
+     * Check if an answer should be selected by default
+     * ie. The question depending on it is displayed.
+     *
+     * @param mixed $answerID
+     */
+    public function getIsAnswerSelected($answerID): bool
     {
         if ($pathway = $this->getInitialPathway()) {
             return in_array($answerID, $pathway);
@@ -111,16 +109,16 @@ public function getIsAnswerSelected($answerID)
     }
 
     /**
-    * Gets the next step to be displayed in regards to the selected answer.
-    * Used by template to display all the relevant steps from the URL
-    *
-    * @return DecisionTreeStep
-    */
-    public function getNextStepFromSelectedAnswer($stepID)
+     * Gets the next step to be displayed in regards to the selected answer.
+     * Used by template to display all the relevant steps from the URL.
+     *
+     * @param mixed $stepID
+     */
+    public function getNextStepFromSelectedAnswer($stepID): ?DecisionTreeStep
     {
         $step = DecisionTreeStep::get()->byID($stepID);
         if ($step->exists()) {
-            foreach($step->Answers() as $answer) {
+            foreach ($step->Answers() as $answer) {
                 if ($this->getIsAnswerSelected($answer->ID)) {
                     if ($nextStep = $answer->ResultingStep()) {
                         return $nextStep;
@@ -133,13 +131,9 @@ public function getNextStepFromSelectedAnswer($stepID)
     }
 
     /**
-    * Template returned via ajax in case of an error occuring.
-    *
-    * @param string
-    *
-    * @return string
-    */
-    protected function renderError($message = '')
+     * Template returned via ajax in case of an error occuring.
+     */
+    protected function renderError(string $message = ''): string
     {
         return sprintf(
             '<div class="step step--error">
@@ -148,9 +142,8 @@ protected function renderError($message = '')
                     <span class="step-title">Sorry!</span>
                     <span class="step-content"><p>%s</p></span>
                 </div>
-            </div>', 
+            </div>',
             $message
         );
     }
-
 }
diff --git a/src/Forms/DecisionTreeStepPreview.php b/src/Forms/DecisionTreeStepPreview.php
index 997e625..edf2e3f 100644
--- a/src/Forms/DecisionTreeStepPreview.php
+++ b/src/Forms/DecisionTreeStepPreview.php
@@ -2,6 +2,7 @@
 
 namespace DNADesign\SilverStripeElementalDecisionTree\Forms;
 
+use DNADesign\SilverStripeElementalDecisionTree\Model\DecisionTreeStep;
 use SilverStripe\Forms\FormField;
 
 /**
@@ -9,23 +10,22 @@
  * ElementDecisionTree or DecisionTreeStes. It provides a visual way of
  * navigating the tree as well as links to edit/add steps.
  */
-
 class DecisionTreeStepPreview extends FormField
 {
-    protected $step = null;
+    protected ?DecisionTreeStep $step = null;
 
-    public function __construct($name, $step = null)
+    public function __construct($name, ?DecisionTreeStep $step = null)
     {
         $this->step = $step;
         parent::__construct($name);
     }
 
-    public function getStep()
+    public function getStep(): ?DecisionTreeStep
     {
         return $this->step;
     }
 
-    public function setStep($step)
+    public function setStep(?DecisionTreeStep $step): static
     {
         $this->step = $step;
 
diff --git a/src/Forms/HasOneSelectOrCreateField.php b/src/Forms/HasOneSelectOrCreateField.php
index 8038e26..83be76d 100644
--- a/src/Forms/HasOneSelectOrCreateField.php
+++ b/src/Forms/HasOneSelectOrCreateField.php
@@ -2,32 +2,31 @@
 
 namespace DNADesign\SilverStripeElementalDecisionTree\Forms;
 
+use SilverShop\HasOneField\GridFieldHasOneEditButton;
+use SilverShop\HasOneField\HasOneButtonField;
 use SilverStripe\Forms\CompositeField;
 use SilverStripe\Forms\DropdownField;
 use SilverStripe\Forms\FormField;
-use SilverShop\HasOneField\HasOneButtonField;
-use SilverShop\HasOneField\GridFieldHasOneEditButton;
-/**
-* This a wrapper for a slightly enhanced user experience when using the
-* HasOneButtonField class.
-* By default, the HasOneButtonField only allow to create or edit the has_one object
-* This class adds a dropdown to allow to select another object or remove the relation
-* without deleting the object itself.
-* Both fields are wrapped in a CompositeField.
-*
-* @param String | Name of the has_one relationship
-* @param String | Title of the drodpwon field
-* @param FieldList or Array | Options listed in the dropdown
-* @param Object | Current has_one object, if exists
-* @param Object | The object calling this field, required by HasOneButtonField
-*/
 
+/**
+ * This a wrapper for a slightly enhanced user experience when using the
+ * HasOneButtonField class.
+ * By default, the HasOneButtonField only allow to create or edit the has_one object
+ * This class adds a dropdown to allow to select another object or remove the relation
+ * without deleting the object itself.
+ * Both fields are wrapped in a CompositeField.
+ *
+ * @param Name|string of the has_one relationship
+ * @param string|Title of the drodpwon field
+ * @param FieldList or Array | Options listed in the dropdown
+ * @param Current|object has_one object, if exists
+ * @param object|The object calling this field, required by HasOneButtonField
+ */
 class HasOneSelectOrCreateField extends CompositeField
 {
+    protected DropdownField $dropdown;
 
-    protected $dropdown;
-
-    protected $gridfield;
+    protected HasOneButtonField $gridfield;
 
     public function __construct($record, $name, $title, $options, $current, $parent)
     {
@@ -49,21 +48,20 @@ public function __construct($record, $name, $title, $options, $current, $parent)
         if ($current && $current->exists()) {
             $name = ($current->Title) ? $current->Title : $current->Name;
             if ($name) {
-                $button->setButtonName('Edit '.FormField::name_to_label($name));
+                $button->setButtonName('Edit ' . FormField::name_to_label($name));
             }
         } else {
-            $button->setButtonName('Create '.$label);
+            $button->setButtonName('Create ' . $label);
         }
 
         // Set Empty String on dropdown
-        $dropdown->setEmptyString('Select '.$label);
+        $dropdown->setEmptyString('Select ' . $label);
 
-        parent::__construct(array($this->dropdown, $this->gridfield));
+        parent::__construct([$this->dropdown, $this->gridfield]);
     }
 
-    public function getRelationName()
+    public function getRelationName(): string
     {
-        return $this->name.'ID';
+        return $this->name . 'ID';
     }
-
 }
diff --git a/src/Model/DecisionTreeAnswer.php b/src/Model/DecisionTreeAnswer.php
index cf0a097..5821688 100644
--- a/src/Model/DecisionTreeAnswer.php
+++ b/src/Model/DecisionTreeAnswer.php
@@ -2,32 +2,32 @@
 
 namespace DNADesign\SilverStripeElementalDecisionTree\Model;
 
-use SilverStripe\ORM\DataObject;
+use DNADesign\SilverStripeElementalDecisionTree\Forms\HasOneSelectOrCreateField;
 use SilverStripe\Control\Controller;
 use SilverStripe\Forms\LiteralField;
-use DNADesign\SilverStripeElementalDecisionTree\Forms\HasOneSelectOrCreateField;
+use SilverStripe\ORM\DataObject;
 
 class DecisionTreeAnswer extends DataObject
 {
-    private static $db = [
+    private static array $db = [
         'Title' => 'Varchar(255)',
-        'Sort' => 'Int'
+        'Sort' => 'Int',
     ];
 
-    private static $has_one = [
+    private static array $has_one = [
         'Question' => DecisionTreeStep::class,
-        'ResultingStep' => DecisionTreeStep::class
+        'ResultingStep' => DecisionTreeStep::class,
     ];
 
-    private static $summary_fields = [
+    private static array $summary_fields = [
         'ID' => 'ID',
         'Title' => 'Title',
-        'ResultingStep.Title' => 'Resulting Step'
+        'ResultingStep.Title' => 'Resulting Step',
     ];
 
-    private static $table_name = 'DecisionTreeAnswer';
+    private static string $table_name = 'DecisionTreeAnswer';
 
-    private static $default_sort = 'Sort ASC';
+    private static string $default_sort = 'Sort ASC';
 
     public function getCMSFields()
     {
@@ -55,10 +55,15 @@ public function getCMSFields()
             }
 
             $stepSelector = HasOneSelectOrCreateField::create(
-                $this, 'ResultingStep', 'If selected, go to', $steps, $this->ResultingStep(), $this
+                $this,
+                'ResultingStep',
+                'If selected, go to',
+                $steps,
+                $this->ResultingStep(),
+                $this
             );
 
-            $fields->addFieldsToTab('Root.Main', $stepSelector);
+            $fields->addFieldToTab('Root.Main', $stepSelector);
         } else {
             $info = LiteralField::create('info', sprintf(
                 '<p class="message info notice">%s</p>',
@@ -87,38 +92,38 @@ public function canEdit($member = null)
     }
 
     /**
-     * Can only delete an answer that doesn't have a dependant question
+     * Can only delete an answer that doesn't have a dependant question.
+     *
+     * @param null|mixed $member
      */
     public function canDelete($member = null)
     {
         $canDelete = singleton(ElementDecisionTree::class)->canDelete($member);
 
-        return ($canDelete && !$this->ResultingStep()->exists());
+        return $canDelete && !$this->ResultingStep()->exists();
     }
 
     /**
-    * Used as breadcrumbs on the parent Step
-    *
-    * @return String
-    */
-    public function TitleWithQuestion()
+     * Used as breadcrumbs on the parent Step.
+     */
+    public function TitleWithQuestion(): ?string
     {
         $title = $this->Title;
         if ($this->Question()->exists()) {
             $title = sprintf('%s > %s', $this->Question()->Title, $title);
         }
+
         return $title;
     }
 
     /**
-    * Create a link that allowd to edit this object in the CMS
-    * To do this, it first finds its parent question
-    * then rewind the tree up to the element
-    * then append its edit url to the edit url of its parent question
-    *
-    * @return String
-    */
-    public function CMSEditLink() {
+     * Create a link that allowd to edit this object in the CMS
+     * To do this, it first finds its parent question
+     * then rewind the tree up to the element
+     * then append its edit url to the edit url of its parent question.
+     */
+    public function getCMSEditLink(): ?string
+    {
         if ($this->Question()->exists()) {
             $origin = $this->Question()->getTreeOrigin();
 
@@ -126,39 +131,33 @@ public function CMSEditLink() {
                 $root = $origin->ParentElement();
 
                 if ($root) {
-                    $url = Controller::join_links(
+                    return Controller::join_links(
                         $root->CMSEditFirstStepLink(),
                         $this->Question()->getRecursiveEditPath(),
                         $this->getRecursiveEditPathForSelf()
                     );
-
-                    return $url;
                 }
             }
         }
+
+        return parent::getCMSEditLink();
     }
 
     /**
-    * Construct the link tp create a new ResultingStep for this answer
-    *
-    * @return String
-    */
-    public function CMSAddStepLink()
+     * Construct the link tp create a new ResultingStep for this answer.
+     */
+    public function CMSAddStepLink(): string
     {
-        $link = Controller::join_links(
-            $this->CMSEditLink(),
+        return Controller::join_links(
+            $this->getCMSEditLink(),
             'itemEditForm/field/ResultingStep/item/new'
         );
-
-        return $link;
     }
 
     /**
-    * Recursively construct the link to edit this object
-    *
-    * @return String
-    */
-    public function getRecursiveEditPath()
+     * Recursively construct the link to edit this object.
+     */
+    public function getRecursiveEditPath(): string
     {
         $path = sprintf('ItemEditForm/field/Answers/item/%s/', $this->ID);
 
@@ -173,11 +172,9 @@ public function getRecursiveEditPath()
     }
 
     /**
-    * Return only the url segment to edit this object
-    *
-    * @return String
-    */
-    public function getRecursiveEditPathForSelf()
+     * Return only the url segment to edit this object.
+     */
+    public function getRecursiveEditPathForSelf(): string
     {
         return sprintf('ItemEditForm/field/Answers/item/%s/', $this->ID);
     }
diff --git a/src/Model/DecisionTreeStep.php b/src/Model/DecisionTreeStep.php
index ebe135a..9da73bd 100644
--- a/src/Model/DecisionTreeStep.php
+++ b/src/Model/DecisionTreeStep.php
@@ -2,53 +2,55 @@
 
 namespace DNADesign\SilverStripeElementalDecisionTree\Model;
 
-use SilverStripe\ORM\DataObject;
-use SilverStripe\Forms\CheckboxField;
-use SilverStripe\ORM\ArrayList;
-use SilverStripe\ORM\FieldType\DBField;
+use DNADesign\SilverStripeElementalDecisionTree\Forms\DecisionTreeStepPreview;
 use SilverStripe\Control\Controller;
-use SilverStripe\Forms\ReadOnlyField;
+use SilverStripe\Forms\CheckboxField;
 use SilverStripe\Forms\GridField\GridField;
-use SilverStripe\Forms\OptionsetField;
 use SilverStripe\Forms\GridField\GridFieldConfig_RecordEditor;
+use SilverStripe\Forms\OptionsetField;
+use SilverStripe\Forms\ReadOnlyField;
+use SilverStripe\Model\List\ArrayList;
+use SilverStripe\Model\List\SS_List;
+use SilverStripe\ORM\DataObject;
+use SilverStripe\ORM\FieldType\DBField;
+use SilverStripe\ORM\FieldType\DBHTMLText;
 use Symbiote\GridFieldExtensions\GridFieldOrderableRows;
 use UncleCheese\DisplayLogic\Forms\Wrapper as DisplayLogicWrapper;
-use DNADesign\SilverStripeElementalDecisionTree\Forms\DecisionTreeStepPreview;
 
 class DecisionTreeStep extends DataObject
 {
-    private static $db = [
+    private static array $db = [
         'Title' => 'Varchar(255)',
         'Type' => "Enum('Question, Result')",
         'Content' => 'HTMLText',
-        'HideTitle' => 'Boolean'
+        'HideTitle' => 'Boolean',
     ];
 
-    private static $has_many = [
-        'Answers' => DecisionTreeAnswer::class.'.Question'
+    private static array $has_many = [
+        'Answers' => DecisionTreeAnswer::class . '.Question',
     ];
 
-    private static $owns = [
-        'Answers'
+    private static array $owns = [
+        'Answers',
     ];
 
-    private static $cascade_deletes = [
-        'Answers'
+    private static array $cascade_deletes = [
+        'Answers',
     ];
 
-    private static $table_name = 'DecisionTreeStep';
+    private static string $table_name = 'DecisionTreeStep';
 
-    private static $belongs_to = [
+    private static array $belongs_to = [
         'ParentAnswer' => DecisionTreeAnswer::class,
-        'ParentElement' => ElementDecisionTree::class
+        'ParentElement' => ElementDecisionTree::class,
     ];
 
-    private static $summary_fields = [
+    private static array $summary_fields = [
         'ID' => 'ID',
-        'Title' => 'Title'
+        'Title' => 'Title',
     ];
 
-    private static $default_result_title = 'Our recommendation';
+    private static string $default_result_title = 'Our recommendation';
 
     public function getCMSFields()
     {
@@ -59,7 +61,7 @@ public function getCMSFields()
 
         $fields->removeByName('Answers');
 
-        $fields->replaceField('Type', $type = OptionsetField::create('Type', 'Type' ,$this->dbObject('Type')->enumValues()));
+        $fields->replaceField('Type', $type = OptionsetField::create('Type', 'Type', $this->dbObject('Type')->enumValues()));
 
         // Allow to hide the title only on Result
         $hideTitle = CheckboxField::create('HideTitle', 'Hide title');
@@ -94,9 +96,9 @@ public function getCMSFields()
     }
 
     /**
-    * Set default title on Result steps
-    */
-    public function onBeforeWrite()
+     * Set default title on Result steps.
+     */
+    public function onBeforeWrite(): void
     {
         if ($this->Type == 'Result' && !$this->Title) {
             $this->Title = $this->config()->default_result_title;
@@ -122,26 +124,22 @@ public function canEdit($member = null)
 
     public function canDelete($member = null)
     {
-        $canDelete = singleton(ElementDecisionTree::class)->canDelete($member);
-
-        return $canDelete;
+        return singleton(ElementDecisionTree::class)->canDelete($member);
     }
 
     /**
-    * Return a readable list of the answer title and the title of the question
-    * which will be displayed if the answer is selected
-    * Used for Gridfield
-    *
-    * @return HTMLText
-    */
-    public function getAnswerTreeForGrid()
+     * Return a readable list of the answer title and the title of the question
+     * which will be displayed if the answer is selected
+     * Used for Gridfield.
+     */
+    public function getAnswerTreeForGrid(): DBField|DBHTMLText
     {
         $output = '';
         if ($this->Answers()->Count()) {
-            foreach($this->Answers() as $answer) {
+            foreach ($this->Answers() as $answer) {
                 $output .= $answer->Title;
                 if ($answer->ResultingStep()) {
-                    $output .= ' => '.$answer->ResultingStep()->Title;
+                    $output .= ' => ' . $answer->ResultingStep()->Title;
                 }
                 $output .= '<br/>';
             }
@@ -151,14 +149,12 @@ public function getAnswerTreeForGrid()
     }
 
     /**
-    * Outputs an optionset to allow user to select an answer to the question
-    *
-    * @return OptionsetField
-    */
-    public function getAnswersOptionset()
+     * Outputs an optionset to allow user to select an answer to the question.
+     */
+    public function getAnswersOptionset(): OptionsetField
     {
-        $source = array();
-        foreach($this->Answers() as $answer) {
+        $source = [];
+        foreach ($this->Answers() as $answer) {
             $source[$answer->ID] = $answer->Title;
         }
 
@@ -166,22 +162,20 @@ public function getAnswersOptionset()
     }
 
     /**
-    * Return the DecisionAnswer rsponsible for displaying this step
-    *
-    * @return DecisionTreeAnswer
-    */
-    public function getParentAnswer()
+     * Return the DecisionAnswer rsponsible for displaying this step.
+     */
+    public function getParentAnswer(): ?DecisionTreeAnswer
     {
-        return DecisionTreeAnswer::get()->filter('ResultingStepID', $this->ID)->First();
+        return DecisionTreeAnswer::get()->filter('ResultingStepID', $this->ID)->first();
     }
 
     /**
-    * Return the list of DecisionTreeAnswer ID
-    * leading to this step being displayed
-    *
-    * @return Array
-    */
-    public function getAnswerPathway(&$idList = array())
+     * Return the list of DecisionTreeAnswer ID
+     * leading to this step being displayed.
+     *
+     * @param mixed $idList
+     */
+    public function getAnswerPathway(&$idList = []): array
     {
         if ($answer = $this->getParentAnswer()) {
             array_push($idList, $answer->ID);
@@ -194,12 +188,12 @@ public function getAnswerPathway(&$idList = array())
     }
 
     /**
-    * Return the list of DecisionTreeStep ID
-    * leading to this step being displayed
-    *
-    * @return Array
-    */
-    public function getQuestionPathway(&$idList = array())
+     * Return the list of DecisionTreeStep ID
+     * leading to this step being displayed.
+     *
+     * @param mixed $idList
+     */
+    public function getQuestionPathway(&$idList = []): array
     {
         array_push($idList, $this->ID);
         if ($answer = $this->getParentAnswer()) {
@@ -212,46 +206,43 @@ public function getQuestionPathway(&$idList = array())
     }
 
     /**
-    * Builds an array of question and answers leading to this Step
-    * Each entry is an array which key is either 'question' or 'answer'
-    * and value is the ID of the object
-    * Note: the array is in reverse order
-    *
-    * @return Array
-    */
-    public function getFullPathway(&$path = array())
+     * Builds an array of question and answers leading to this Step
+     * Each entry is an array which key is either 'question' or 'answer'
+     * and value is the ID of the object
+     * Note: the array is in reverse order.
+     *
+     * @param mixed $path
+     */
+    public function getFullPathway(&$path = []): array
     {
         if ($answer = $this->getParentAnswer()) {
-            array_push($path, array('question' => $this->ID));
-            array_push($path, array('answer' => $answer->ID));
+            array_push($path, ['question' => $this->ID]);
+            array_push($path, ['answer' => $answer->ID]);
             if ($question = $answer->Question()) {
                 $question->getFullPathway($path);
             }
         } else {
-            array_push($path, array('question' => $this->ID));
+            array_push($path, ['question' => $this->ID]);
         }
 
         return $path;
     }
 
     /**
-    * Find the very first DecisionStep in the tree
-    *
-    * @return DecisionTreeStep
-    */
-    public function getTreeOrigin()
+     * Find the very first DecisionStep in the tree.
+     */
+    public function getTreeOrigin(): ?DecisionTreeStep
     {
         $pathway = array_reverse($this->getQuestionPathway());
+
         return DecisionTreeStep::get()->byID($pathway[0]);
     }
 
     /**
-    * Return this step position in the pathway
-    * Used to number step on the front end
-    *
-    * @return Int
-    */
-    public function getPositionInPathway()
+     * Return this step position in the pathway
+     * Used to number step on the front end.
+     */
+    public function getPositionInPathway(): int
     {
         $pathway = array_reverse($this->getFullPathway());
         // Pathway has both questions and answers
@@ -264,13 +255,11 @@ public function getPositionInPathway()
     }
 
     /**
-    * Return a DataList of DecisionTreeStep that do not belong to a Tree
-    *
-    * @return SS_List
-    */
-    public static function get_orphans()
+     * Return a DataList of DecisionTreeStep that do not belong to a Tree.
+     */
+    public static function get_orphans(): SS_List
     {
-        $orphans = DecisionTreeStep::get()->filterByCallback(function($item) {
+        $orphans = DecisionTreeStep::get()->filterByCallback(function ($item) {
             return !$item->belongsToTree();
         });
 
@@ -282,14 +271,12 @@ public static function get_orphans()
     }
 
     /**
-    * Return a DataList of all DecisionTreeStep that do not belong to an answer
-    * ie. are the first child of a element
-    *
-    * @return SS_List
-    */
-    public static function get_initial_steps()
+     * Return a DataList of all DecisionTreeStep that do not belong to an answer
+     * ie. are the first child of a element.
+     */
+    public static function get_initial_steps(): ?SS_List
     {
-        $initial = DecisionTreeStep::get()->filterByCallback(function($item) {
+        $initial = DecisionTreeStep::get()->filterByCallback(function ($item) {
             return !$item->belongsToAnswer();
         });
 
@@ -298,41 +285,30 @@ public static function get_initial_steps()
         }
 
         return DecisionTreeStep::get()->filter([
-            'ID' => $initial->column('ID')
+            'ID' => $initial->column('ID'),
         ])->exclude('Type', 'Result');
     }
 
-    /**
-    *
-    */
-    public function belongsToTree()
+    public function belongsToTree(): bool
     {
-        return ($this->belongsToElement() || $this->belongsToAnswer());
+        return $this->belongsToElement() || $this->belongsToAnswer();
     }
 
-    /**
-    *
-    */
-    public function belongsToElement()
+    public function belongsToElement(): bool
     {
-        return (ElementDecisionTree::get()->filter('FirstStepID', $this->ID)->Count() > 0);
+        return ElementDecisionTree::get()->filter('FirstStepID', $this->ID)->Count() > 0;
     }
 
-    /**
-    *
-    */
-    public function belongsToAnswer()
+    public function belongsToAnswer(): bool
     {
-        return ($this->ParentAnswer() && $this->ParentAnswer()->exists());
+        return $this->ParentAnswer() && $this->ParentAnswer()->exists();
     }
 
     /**
-    * Checks if this object is currently being edited in the CMS
-    * by comparing its ID with the one in the request
-    *
-    * @return Boolean
-    */
-    public function IsCurrentlyEdited()
+     * Checks if this object is currently being edited in the CMS
+     * by comparing its ID with the one in the request.
+     */
+    public function IsCurrentlyEdited(): bool
     {
         $request = Controller::curr()->getRequest();
         $class = $request->param('FieldName');
@@ -341,50 +317,48 @@ public function IsCurrentlyEdited()
         $stepRelationships = ['ResultingStep', 'FirstStep'];
 
         if ($currentID && in_array($class, $stepRelationships)) {
-            return  $currentID == $this->ID;
+            return $currentID == $this->ID;
         }
 
         return false;
     }
 
     /**
-    * Create a link that allowd to edit this object in the CMS
-    * To do this, it rewinds the tree up to the element
-    * then append its edit url to the edit url of its parent question
-    *
-    * @return String
-    */
-    public function CMSEditLink() {
+     * Create a link that allowd to edit this object in the CMS
+     * To do this, it rewinds the tree up to the element
+     * then append its edit url to the edit url of its parent question.
+     */
+    public function getCMSEditLink(): ?string
+    {
         $origin = $this->getTreeOrigin();
         if ($origin) {
             $root = $origin->ParentElement();
             if ($root) {
-                $url = Controller::join_links($root->CMSEditFirstStepLink(), $this->getRecursiveEditPath());
-                return $url;
+                return Controller::join_links($root->CMSEditFirstStepLink(), $this->getRecursiveEditPath());
             }
         }
+
+        return parent::getCMSEditLink();
     }
 
     /**
-    * Build url to allow to edit this object
-    *
-    * @return String
-    */
-    public function getRecursiveEditPath()
+     * Build url to allow to edit this object.
+     */
+    public function getRecursiveEditPath(): string
     {
         $pathway = array_reverse($this->getFullPathway());
         unset($pathway[0]); // remove first question
 
         $url = '';
-        foreach($pathway as $step) {
+        foreach ($pathway as $step) {
             if (is_array($step) && !empty($step)) {
                 $type = array_keys($step)[0];
                 $id = $step[$type];
 
                 if ($type == 'question') {
-                    $url .= '/ItemEditForm/field/ResultingStep/item/'.$id;
-                } else if ($type == 'answer') {
-                    $url .= '/ItemEditForm/field/Answers/item/'.$id;
+                    $url .= '/ItemEditForm/field/ResultingStep/item/' . $id;
+                } elseif ($type == 'answer') {
+                    $url .= '/ItemEditForm/field/Answers/item/' . $id;
                 }
             }
         }
diff --git a/src/Model/ElementDecisionTree.php b/src/Model/ElementDecisionTree.php
index 0ba6ac5..8e025e5 100644
--- a/src/Model/ElementDecisionTree.php
+++ b/src/Model/ElementDecisionTree.php
@@ -3,33 +3,33 @@
 namespace DNADesign\SilverStripeElementalDecisionTree\Model;
 
 use DNADesign\Elemental\Models\BaseElement;
-use DNADesign\SilverStripeElementalDecisionTree\Forms\HasOneSelectOrCreateField;
 use DNADesign\SilverStripeElementalDecisionTree\Forms\DecisionTreeStepPreview;
-use SilverStripe\Control\Controller;
+use DNADesign\SilverStripeElementalDecisionTree\Forms\HasOneSelectOrCreateField;
 use SilverStripe\CMS\Controllers\CMSPageEditController;
+use SilverStripe\Control\Controller;
 use SilverStripe\Forms\LiteralField;
 
 class ElementDecisionTree extends BaseElement
 {
-    private static $title = "Decision Tree";
+    private static string $title = 'Decision Tree';
 
-    private static $description = "Display a decision tree with questions and results";
+    private static string $class_description = 'Display a decision tree with questions and results';
 
-    private static $enable_title_in_template = true;
+    private static bool $enable_title_in_template = true;
 
-    private static $icon = 'font-icon-flow-tree';
+    private static string $icon = 'font-icon-flow-tree';
 
-    private static $db = [
-        'Introduction' => 'HTMLText'
+    private static array $db = [
+        'Introduction' => 'HTMLText',
     ];
 
-    private static $has_one = [
-        'FirstStep' => DecisionTreeStep::class
+    private static array $has_one = [
+        'FirstStep' => DecisionTreeStep::class,
     ];
 
-    private static $table_name = 'ElementDecisionTree';
+    private static string $table_name = 'ElementDecisionTree';
 
-    private static $inline_editable = false;
+    private static bool $inline_editable = false;
 
     public function getType()
     {
@@ -46,7 +46,12 @@ public function getCMSFields()
 
         if ($this->IsInDB()) {
             $stepSelector = HasOneSelectOrCreateField::create(
-                $this, 'FirstStep', 'First Step', DecisionTreeStep::get_initial_steps()->map(), $this->FirstStep(), $this
+                $this,
+                'FirstStep',
+                'First Step',
+                DecisionTreeStep::get_initial_steps()->map(),
+                $this->FirstStep(),
+                $this
             );
 
             $fields->addFieldToTab('Root.Main', $stepSelector);
@@ -65,16 +70,16 @@ public function getCMSFields()
     }
 
     /**
-    * Builds the Edit Link to the FirstStep of this element
-    *
-    * @return string
-    */
-    public function CMSEditFirstStepLink()
+     * Builds the Edit Link to the FirstStep of this element.
+     */
+    public function CMSEditFirstStepLink(): ?string
     {
         $page = $this->getPage();
         $firstStep = $this->FirstStep();
 
-        if (!$page || !$page->exists() || !$firstStep->exists()) return null;
+        if (!$page || !$page->exists() || !$firstStep->exists()) {
+            return null;
+        }
 
         return Controller::join_links(
             singleton(CMSPageEditController::class)->Link('EditForm'),