fix NPE with deserializing custom field empty set

Author: jenschude

commercetools/commercetools-sdk-java-api/src/main/java/com/commercetools/api/json/CustomFieldDeserializer.java

@@ -143,6 +143,9 @@ private TypeReference<?> typeRef(JsonNode valueNode) {
     }
 
     private ElemType elemType(JsonNode valueNode) {
+        if (valueNode == null) {
+            return ElemType.JSON_NODE;
+        }
         JsonNodeType valueNodeType = valueNode.getNodeType();
         switch (valueNodeType) {
             case OBJECT:

commercetools/commercetools-sdk-java-api/src/test/java/com/commercetools/CustomFieldsTest.java

@@ -8,10 +8,12 @@
 import java.time.LocalDate;
 import java.time.LocalTime;
 import java.time.ZonedDateTime;
+import java.util.List;
 import java.util.Map;
 
 import com.commercetools.api.models.common.LocalizedString;
 import com.commercetools.api.models.common.TypedMoney;
+import com.commercetools.api.models.order.Order;
 import com.commercetools.api.models.product.ProductReference;
 import com.commercetools.api.models.type.CustomFieldEnumValue;
 import com.commercetools.api.models.type.CustomFieldLocalizedEnumValue;
@@ -70,5 +72,13 @@ public void fields() throws IOException {
             number -> assertThat(number).isEqualTo(11.0));
         assertThat(fields.get("set-reference")).asList().first().isInstanceOf(ProductReference.class);
         assertThat(fields.get("set-money")).asList().first().isInstanceOf(TypedMoney.class);
+        assertThat(fields.get("set-empty")).asList().isEmpty();
+    }
+
+    @Test
+    public void emptyField() throws IOException {
+        Order order = JsonUtils.fromJsonString(stringFromResource("orderlineitem.json"), Order.class);
+
+        assertThat(order.getLineItems().get(0).getCustom().getFields().values().get("empty")).isInstanceOf(List.class);
     }
 }

commercetools/commercetools-sdk-java-api/src/test/resources/attributes.json

@@ -153,6 +153,10 @@
                     }
                 ]
             ]
+        },
+        {
+            "name": "set-empty",
+            "value": []
         }
     ]
 }

commercetools/commercetools-sdk-java-api/src/test/resources/customfields.json

@@ -79,6 +79,7 @@
         ],
         "set-boolean": [
             true
-        ]
+        ],
+        "set-empty": []
     }
 }

commercetools/commercetools-sdk-java-api/src/test/resources/orderlineitem.json

@@ -0,0 +1,15 @@
+{
+    "lineItems": [
+        {
+            "custom": {
+                "type": {
+                    "typeId" : "type",
+                    "id": "12345"
+                },
+                "fields": {
+                    "empty": []
+                }
+            }
+        }
+    ]
+}