created a doc

Author: rohitmishra209

src/lib/models/stack.php

@@ -156,9 +156,16 @@ public function getEnvironment() {
         return $this->environment;
     }
 
+     /*
+     * This call returns comprehensive information of all the content types available in a particular stack in your account.
+     * @return Stack
+     * */
     public function getContentTypes($params) {
-        $myArray = json_decode($params, true);
-        $this->_query = $myArray;
+        if($params && $params !== "undefined") {
+            $myArray = json_decode($params, true);
+            $this->_query = $myArray;
+        }
+        
         return \Contentstack\Utility\contentstackRequest($this, "getcontentTypes");
     }
 }