Fix null relation transformers

src/generator/default/transformer.php

@@ -36,10 +36,14 @@ public function transform(<?=$transformer->dbModel->getClassName()?> $model)
     public function include<?=$relation->getCamelName()?>(<?=$transformer->dbModel->getClassName()?> $model)
     {
         $relation = $model-><?=Inflector::variablize($relation->getName())?>;
-        $transformer = new <?=Inflector::singularize($relation->getClassName())?>Transformer();
 <?php if ($relation->isHasOne()):?>
+        if ($relation === null) {
+            return $this->null();
+        }
+        $transformer = new <?=Inflector::singularize($relation->getClassName())?>Transformer();
         return $this->item($relation, $transformer, '<?=$transformer->makeResourceKey($relation->getClassKey())?>');
 <?php else:?>
+        $transformer = new <?=Inflector::singularize($relation->getClassName())?>Transformer();
         return $this->collection($relation, $transformer, '<?=$transformer->makeResourceKey($relation->getClassKey())?>');
 <?php endif;?>
     }

tests/specs/blog_jsonapi/transformers/CommentTransformer.php

@@ -17,13 +17,19 @@ public function transform(Comment $model)
     public function includePost(Comment $model)
     {
         $relation = $model->post;
+        if ($relation === null) {
+            return $this->null();
+        }
         $transformer = new PostTransformer();
         return $this->item($relation, $transformer, 'posts');
     }
 
     public function includeUser(Comment $model)
     {
         $relation = $model->user;
+        if ($relation === null) {
+            return $this->null();
+        }
         $transformer = new UserTransformer();
         return $this->item($relation, $transformer, 'users');
     }

tests/specs/blog_jsonapi/transformers/PostTransformer.php

@@ -17,13 +17,19 @@ public function transform(Post $model)
     public function includeCategory(Post $model)
     {
         $relation = $model->category;
+        if ($relation === null) {
+            return $this->null();
+        }
         $transformer = new CategoryTransformer();
         return $this->item($relation, $transformer, 'categories');
     }
 
     public function includeAuthor(Post $model)
     {
         $relation = $model->author;
+        if ($relation === null) {
+            return $this->null();
+        }
         $transformer = new UserTransformer();
         return $this->item($relation, $transformer, 'users');
     }