fix: ensure that extended fields in MutableObjectType instances are found

Author: xyng

src/Types/MutableObjectType.php

@@ -4,6 +4,7 @@
 
 namespace TheCodingMachine\GraphQLite\Types;
 
+use GraphQL\Type\Definition\FieldDefinition;
 use GraphQL\Type\Definition\ObjectType;
 
 /**
@@ -24,4 +25,19 @@ public function __construct(array $config, ?string $className = null)
         parent::__construct($config);
         $this->className = $className;
     }
+
+    public function findField(string $name): ?FieldDefinition
+    {
+        $field = parent::findField($name);
+        if ($field) {
+            return $field;
+        }
+
+        $fields = $this->getFields();
+        if (! isset($fields[$name])) {
+            return null;
+        }
+
+        return $fields[$name];
+    }
 }