Fix arguments transformer when data is not set

When data for an input doesn't exist (ie. The property is not set in the data), use the default value of the input property or null if is doesn't have one.

Author: Vincz

src/Transformer/ArgumentsTransformer.php

@@ -102,7 +102,7 @@ private function populateObject(Type $type, $data, bool $multiple, ResolveInfo $
             $fields = $type->getFields();
 
             foreach ($fields as $name => $field) {
-                $fieldData = $this->accessor->getValue($data, sprintf('[%s]', $name));
+                $fieldData = \array_key_exists($name, $data) ? $this->accessor->getValue($data, sprintf('[%s]', $name)) : $this->accessor->getValue($instance, $name);
                 $fieldType = $field->getType();
 
                 if ($fieldType instanceof NonNull) {

tests/Transformer/ArgumentsTransformerTest.php

@@ -125,6 +125,9 @@ public function testPopulating(): void
         $this->assertEquals($res->field1, $data['field1']);
         $this->assertEquals($res->field2, $data['field2']);
         $this->assertEquals($res->field3, $data['field3']);
+        $this->assertEquals($res->field4, "default_value_when_not_set_in_data");
+        $this->assertEquals($res->field5, []);
+        $this->assertEquals($res->field6, null);
 
         $data = [
             'field1' => [

tests/Transformer/InputType1.php

@@ -20,4 +20,16 @@ final class InputType1
      * @var mixed
      */
     public $field3;
+
+    /**
+     * @var mixed
+     */
+    public $field4 = "default_value_when_not_set_in_data";
+
+    /**
+     * @var array
+     */
+    public $field5 = [];
+
+    public $field6;
 }