fix uses default + toString pb

Author: jcheron

src/Ubiquity/creator/HasUsesTrait.php

@@ -2,7 +2,7 @@
 namespace Ubiquity\creator;
 
 trait HasUsesTrait {
-	protected $uses;
+	protected $uses=[];
 	public function getUses(){
 		return \array_keys($this->uses);
 	}

src/Ubiquity/orm/creator/Model.php

@@ -225,7 +225,7 @@ private function getToStringField() {
 		$result = null;
 
 		foreach ($this->members as $member) {
-			if ($member->getDbType() !== 'mixed' && ! $member->isPrimary()) {
+			if ($member->getDbType() !== 'mixed' && $member->isNullable() !== true && ! $member->isPrimary()) {
 				$memberName = $member->getName();
 				if (! $member->isPassword()) {
 					$result = $memberName;