Fix, model builder setter will not try to cast value if already the proper type

lib/model-builder.js

@@ -380,7 +380,7 @@ ModelBuilder.prototype.define = function defineClass(className, properties, sett
             } else {
               // Assume the type constructor handles Constructor() call
               // If not, we should call new DataType(value).valueOf();
-              this.__data[propertyName] = DataType(value);
+              this.__data[propertyName] = (value instanceof DataType) ? value : DataType(value);
             }
           }
         }