[fixes #228] Sending an array for fields with a single value is silently ignored by zendesk APIs

Author: aheritier

src/main/java/org/zendesk/client/v2/model/CustomFieldValue.java

@@ -17,7 +17,8 @@ public class CustomFieldValue implements Serializable {
 
     private Long id;
 
-    @JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
+    @JsonFormat(with = {JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY,
+            JsonFormat.Feature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED})
     private String[] value;
 
     public CustomFieldValue() {