Fix slug for data file

content/core.page/test.yaml

@@ -1,2 +1,4 @@
 - title: Foo
   content: bar
+- title: Bar
+  content: foo

yamdl_playground/core/models.py

@@ -4,6 +4,6 @@ class Page(models.Model):
     __yamdl__ = True
 
     title = models.CharField(max_length=255)
-    slug = models.CharField(max_length=128, unique=True, db_index=True)
+    slug = models.CharField(max_length=128, unique=True, db_index=True, default=None, null=True)
 
     content = models.TextField()

yamdl_playground/core/utils.py

@@ -2,5 +2,7 @@ from yamdl.loader import ModelLoader
 
 class CustomYamdlLoader(ModelLoader):
     def load_fixture(self, model_class, data, file_path):
-        data["slug"] = file_path.stem
+        if file_path.suffix not in self.EXT_YAML:
+            data["slug"] = file_path.stem
+
         super().load_fixture(model_class, data, file_path)