fixup! Fix attr reader to force the intended values for source and target shas

app/models/merge_request.rb

@@ -238,15 +238,11 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def target_branch_sha
-    return @target_branch_sha if defined?(@target_branch_sha)
-
-    target_branch_head.try(:sha)
+    @target_branch_sha || target_branch_head.try(:sha)
   end
 
   def source_branch_sha
-    return @source_branch_sha if defined?(@source_branch_sha)
-
-    source_branch_head.try(:sha)
+    @source_branch_sha || source_branch_head.try(:sha)
   end
 
   def diff_refs