1 files changed, 16 insertions, 0 deletions
diff --git a/app/graphql/mutations/notes/create/diff_note.rb b/app/graphql/mutations/notes/create/diff_note.rb
index 9b5f3092006..019e7cb8623 100644
--- a/app/graphql/mutations/notes/create/diff_note.rb
+++ b/app/graphql/mutations/notes/create/diff_note.rb
@@ -11,6 +11,22 @@ module Mutations
                   required: true,
                   description: copy_field_description(Types::Notes::NoteType, :position)
 
+        def ready?(**args)
+          # As both arguments are optional, validate here that one of the
+          # arguments are present.
+          #
+          # This may be able to be done using InputUnions in the future
+          # if this RFC is merged:
+          # https://github.com/graphql/graphql-spec/blob/master/rfcs/InputUnion.md
+
+          if args[:position].to_hash.values_at(:old_line, :new_line).compact.blank?
+            raise Gitlab::Graphql::Errors::ArgumentError,
+                  'position oldLine or newLine arguments are required'
+          end
+
+          super(**args)
+        end
+
         private
 
         def create_note_params(noteable, args)