return back instance fields so as not to overwrite not required fields on None

graphene_django/forms/mutation.py

@@ -186,6 +186,18 @@ class DjangoModelFormMutation(BaseDjangoFormMutation):
         kwargs = {cls._meta.return_field_name: obj}
         return cls(errors=[], **kwargs)
 
+    @classmethod
+    def get_form_kwargs(cls, root, info, **input):
+        kwargs = super().get_form_kwargs(root, info, **input)
+        instance = kwargs.get('instance')
+        if not instance:
+            return kwargs
+
+        for field in kwargs.get('instance')._meta.fields:
+            if field.name not in kwargs['data'] and field.name != 'id':
+                kwargs['data'][field.name] = getattr(instance, field.name)
+        return kwargs
+
 
 def _set_errors_flag_to_context(info):
     # This is not ideal but necessary to keep the response errors empty