fixed return type of RendererInterface

Structural/Decorator/RenderInJson.php

@@ -10,12 +10,10 @@ class RenderInJson extends Decorator
     /**
      * render data as JSON.
      *
-     * @return mixed|string
+     * @return string
      */
     public function renderData()
     {
-        $output = $this->wrapped->renderData();
-
-        return json_encode($output);
+        return json_encode($this->wrapped->renderData());
     }
 }

Structural/Decorator/RenderInXml.php

@@ -10,17 +10,15 @@ class RenderInXml extends Decorator
     /**
      * render data as XML.
      *
-     * @return mixed|string
+     * @return string
      */
     public function renderData()
     {
-        $output = $this->wrapped->renderData();
-
         // do some fancy conversion to xml from array ...
 
         $doc = new \DOMDocument();
 
-        foreach ($output as $key => $val) {
+        foreach ($this->wrapped->renderData() as $key => $val) {
             $doc->appendChild($doc->createElement($key, $val));
         }
 

Structural/Decorator/RendererInterface.php

@@ -10,7 +10,7 @@ interface RendererInterface
     /**
      * render data.
      *
-     * @return mixed
+     * @return string
      */
     public function renderData();
 }