Allow Response objects with no schema

Fixes #66.

src/drf_yasg/inspectors/view.py

@@ -221,7 +221,7 @@ class SwaggerAutoSchema(ViewInspector):
                 )
             elif isinstance(serializer, openapi.Response):
                 response = serializer
-                if not isinstance(response.schema, openapi.Schema.OR_REF):
+                if hasattr(response, 'schema') and not isinstance(response.schema, openapi.Schema.OR_REF):
                     serializer = force_serializer_instance(response.schema)
                     response.schema = self.serializer_to_schema(serializer)
             elif isinstance(serializer, openapi.Schema.OR_REF):

testproj/snippets/views.py

@@ -1,7 +1,7 @@
 from djangorestframework_camel_case.parser import CamelCaseJSONParser
 from djangorestframework_camel_case.render import CamelCaseJSONRenderer
 from inflection import camelize
-from rest_framework import generics
+from rest_framework import generics, status
 from rest_framework.parsers import FormParser
 
 from drf_yasg import openapi
@@ -62,8 +62,12 @@ class SnippetDetail(generics.RetrieveUpdateDestroyAPIView):
             type=openapi.TYPE_INTEGER,
             description="path parameter override",
             required=True
+        ),
+    ], responses={
+        status.HTTP_204_NO_CONTENT: openapi.Response(
+            description="This should not crash"
         )
-    ])
+    })
     def delete(self, request, *args, **kwargs):
         """delete method docstring"""
         return super(SnippetDetail, self).patch(request, *args, **kwargs)

tests/reference.yaml

@@ -330,7 +330,7 @@ paths:
           type: integer
       responses:
         '204':
-          description: ''
+          description: This should not crash
       tags:
         - snippets
     parameters: