So that st_commits could never be nil

app/models/merge_request_diff.rb

@@ -30,6 +30,10 @@ class MergeRequestDiff < ActiveRecord::Base
     select(column_names - ['st_diffs'])
   end
 
+  def st_commits
+    super || []
+  end
+
   # Collect information about commits and diff from repository
   # and save it to the database as serialized data
   def save_git_content
@@ -83,7 +87,7 @@ class MergeRequestDiff < ActiveRecord::Base
   end
 
   def commits
-    @commits ||= load_commits(st_commits || [])
+    @commits ||= load_commits(st_commits)
   end
 
   def reload_commits
@@ -120,10 +124,8 @@ class MergeRequestDiff < ActiveRecord::Base
   def commits_sha
     if @commits
       commits.map(&:sha)
-    elsif st_commits
-      st_commits.map { |commit| commit[:id] }
     else
-      []
+      st_commits.map { |commit| commit[:id] }
     end
   end