Added passing loaded relationship to value callback (#50167)

Author: dkulyk

src/Illuminate/Http/Resources/ConditionallyLoadsAttributes.php

@@ -266,15 +266,17 @@ protected function whenLoaded($relationship, $value = null, $default = null)
             return value($default);
         }
 
+        $loadedValue = $this->resource->{$relationship};
+
         if (func_num_args() === 1) {
-            return $this->resource->{$relationship};
+            return $loadedValue;
         }
 
-        if ($this->resource->{$relationship} === null) {
+        if ($loadedValue === null) {
             return;
         }
 
-        return value($value);
+        return value($value, $loadedValue);
     }
 
     /**