Fix 404 errors on Merge Request -> new

app/helpers/commits_helper.rb

@@ -65,4 +65,9 @@ module CommitsHelper
     end
   end
 
+  def commit_to_html commit
+    if commit.model
+      escape_javascript(render 'commits/commit', commit: commit)
+    end
+  end
 end

app/views/merge_requests/branch_from.js.haml

 :plain
-  $(".mr_source_commit").html("#{escape_javascript(render 'commits/commit', commit: @commit)}");
+  $(".mr_source_commit").html("#{commit_to_html(@commit)}");

app/views/merge_requests/branch_to.js.haml

 :plain
-  $(".mr_target_commit").html("#{escape_javascript(render 'commits/commit', commit: @commit)}");
-
+  $(".mr_target_commit").html("#{commit_to_html(@commit)}");