diff --git a/graphene_django/forms/converter.py b/graphene_django/forms/converter.py
index 220edc4..9d87811 100644
--- a/graphene_django/forms/converter.py
+++ b/graphene_django/forms/converter.py
@@ -16,21 +16,6 @@ except AttributeError:
 singledispatch = import_single_dispatch()
 
 
-def convert_form_to_input_type(form_class):
-    form = form_class()
-
-    items = {
-        name: convert_form_field(field)
-        for name, field in form.fields.items()
-    }
-
-    return type(
-        '{}Input'.format(form.__class__.__name__),
-        (graphene.InputObjectType, ),
-        items
-    )
-
-
 @singledispatch
 def convert_form_field(field):
     raise ImproperlyConfigured(
diff --git a/graphene_django/forms/mutation.py b/graphene_django/forms/mutation.py
index bbe5f80..49fabb8 100644
--- a/graphene_django/forms/mutation.py
+++ b/graphene_django/forms/mutation.py
@@ -83,7 +83,7 @@ class FormMutation(BaseFormMutation):
     @classmethod
     def perform_mutate(cls, form, info):
         form.save()
-        return cls(errors=None)
+        return cls(errors=[])
 
 
 class ModelFormMutationOptions(FormMutationOptions):
@@ -138,4 +138,4 @@ class ModelFormMutation(BaseFormMutation):
     def perform_mutate(cls, form, info):
         obj = form.save()
         kwargs = {cls._meta.return_field_name: obj}
-        return cls(errors=None, **kwargs)
+        return cls(errors=[], **kwargs)
diff --git a/graphene_django/forms/tests/test_mutation.py b/graphene_django/forms/tests/test_mutation.py
index 5f1ef4a..084b8b0 100644
--- a/graphene_django/forms/tests/test_mutation.py
+++ b/graphene_django/forms/tests/test_mutation.py
@@ -68,8 +68,23 @@ class ModelFormMutationTests(TestCase):
             class Meta:
                 form_class = PetForm
 
-        PetMutation.mutate_and_get_payload(None, None, name='Fluffy')
+        result = PetMutation.mutate_and_get_payload(None, None, name='Fluffy')
 
         self.assertEqual(Pet.objects.count(), 1)
         pet = Pet.objects.get()
         self.assertEqual(pet.name, 'Fluffy')
+        self.assertEqual(result.errors, [])
+
+    def test_model_form_mutation_mutate_invalid_form(self):
+        class PetMutation(ModelFormMutation):
+            class Meta:
+                form_class = PetForm
+
+        result = PetMutation.mutate_and_get_payload(None, None)
+
+        # A pet was not created
+        self.assertEqual(Pet.objects.count(), 0)
+
+        self.assertEqual(len(result.errors), 1)
+        self.assertEqual(result.errors[0].field, 'name')
+        self.assertEqual(result.errors[0].messages, ['This field is required.'])