MAGETWO-56206: API - inconsistency in the Magento response data types

- Force extension_attributes to empty object instead of empty array
- Remove unused imports and docblocks

Author: tjwiebell

lib/internal/Magento/Framework/Reflection/DataObjectProcessor.php

@@ -7,7 +7,6 @@
 
 use Magento\Framework\Api\CustomAttributesDataInterface;
 use Magento\Framework\Phrase;
-use Zend\Code\Reflection\MethodReflection;
 
 /**
  * Data object processor for array serialization using class reflection
@@ -75,7 +74,6 @@ public function buildOutputDataArray($dataObject, $dataObjectType)
         $methods = $this->methodsMapProcessor->getMethodsMap($dataObjectType);
         $outputData = [];
 
-        /** @var MethodReflection $method */
         foreach (array_keys($methods) as $methodName) {
             if (!$this->methodsMapProcessor->isMethodValidForDataField($dataObjectType, $methodName)) {
                 continue;
@@ -99,7 +97,8 @@ public function buildOutputDataArray($dataObject, $dataObjectType)
             if ($key === CustomAttributesDataInterface::CUSTOM_ATTRIBUTES) {
                 $value = $this->customAttributesProcessor->buildOutputDataArray($dataObject, $dataObjectType);
             } elseif ($key === "extension_attributes") {
-                $value = $this->extensionAttributesProcessor->buildOutputDataArray($value, $returnType);
+                $attributeArray = $this->extensionAttributesProcessor->buildOutputDataArray($value, $returnType);
+                $value = empty($attributeArray) ? new \Magento\Framework\DataObject() : $attributeArray;
             } else {
                 if (is_object($value) && !($value instanceof Phrase)) {
                     $value = $this->buildOutputDataArray($value, $returnType);