Updated RequestChanable Interface and Trait

+ Fixed an error that was caused by the use of the "self" type-hint in a trait
+ Added more  type-hints to the `setCaller()` method

src/Core/Interfaces/RequestChainableInterface.php

@@ -28,7 +28,7 @@ interface RequestChainableInterface
      *
      * @return self
      */
-    public function setCaller($object): self;
+    public function setCaller(?object $object);
 
     /**
      * Return the request chain heirarchy

src/Core/Traits/RequestChainable.php

@@ -40,7 +40,7 @@ trait RequestChainable
      *
      * @return self
      */
-    public function setCaller($object): self
+    public function setCaller(?object $object)
     {
         $this->caller = $object;
         return $this;