[10.x] Fix whenAggregated when default is not specified (#49521)

* Fix: whenAggregated should return MissingValue when default is not specified

* Test: whenAggregated should return MissingValue when default is not specified

Author: lovePizza

src/Illuminate/Http/Resources/ConditionallyLoadsAttributes.php

@@ -320,6 +320,10 @@ public function whenCounted($relationship, $value = null, $default = null)
      */
     public function whenAggregated($relationship, $column, $aggregate, $value = null, $default = null)
     {
+        if (func_num_args() < 5) {
+            $default = new MissingValue;
+        }
+        
         $attribute = (string) Str::of($relationship)->snake()->append('_')->append($aggregate)->append('_')->finish($column);
 
         if (! isset($this->resource->getAttributes()[$attribute])) {

tests/Integration/Http/ResourceTest.php

@@ -502,8 +502,6 @@ public function testResourcesMayHaveOptionalRelationshipAggregates()
             'data' => [
                 'id' => 5,
                 'title' => 'Test Title',
-                'average_rating' => null,
-                'minimum_rating' => null,
                 'maximum_rating' => 'Default Value',
             ],
         ]);