don't create MR diff as this can be imported presumably

app/models/merge_request.rb

@@ -45,7 +45,7 @@ class MergeRequest < ActiveRecord::Base
 
   serialize :merge_params, Hash
 
-  after_create :create_merge_request_diff
+  after_create :create_merge_request_diff, unless: :importing
   after_update :update_merge_request_diff
 
   delegate :commits, :diffs, :real_size, to: :merge_request_diff, prefix: nil