Merge branch 'fix-stuck-mr' into 'master'

fix stuck mr

If `locked?` & `locked_at.nil?` is nil return that the merge has been locked long enough and those are old merges stuck in locked state.

Fixes #348. Related to 64874193. Replaces !517.

/cc @DouweM

See merge request !526

CHANGELOG

@@ -76,6 +76,7 @@ v 7.10.0 (unreleased)
   - Bust group page project list cache when namespace name or path changes.
   - Explicitly set image alt-attribute to prevent graphical glitches if gravatars could not be loaded
   - Allow user to choose a public email to show on public profile
+  - Fix stuck Merge Request merging events from old installations (Ben Bodenmiller)
 
 v 7.9.3
   - Contains no changes

app/models/merge_request.rb

@@ -361,6 +361,8 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def locked_long_ago?
-    locked_at && locked_at < (Time.now - 1.day)
+    return false unless locked?
+
+    locked_at.nil? || locked_at < (Time.now - 1.day)
   end
 end