Update Reporter.php

Should have done this check and not return a blank array

Author: carcus88

src/Issue/Reporter.php

@@ -32,6 +32,9 @@ public function jsonSerialize()
                 unset($vars[$key]);
             }
         }
-        return $vars;
+		if(empty($vars)) {
+			return null;
+		}
+		return $vars;
     }
 }