Fix HiddenField stripping in BrowsableAPIRenderer (#5499)

Author: Ryan P Kilby

rest_framework/renderers.py

@@ -557,9 +557,12 @@ def get_raw_data_form(self, data, view, method, request):
                 accepted = self.accepted_media_type
                 context = self.renderer_context.copy()
                 context['indent'] = 4
-                data = {k: v for (k, v) in serializer.data.items()
-                        if not isinstance(serializer.fields[k],
-                                          serializers.HiddenField)}
+
+                # strip HiddenField from output
+                data = serializer.data.copy()
+                for name, field in serializer.fields.items():
+                    if isinstance(field, serializers.HiddenField):
+                        data.pop(name, None)
                 content = renderer.render(data, accepted, context)
             else:
                 content = None