#888 prevent to remove source_branch

app/models/merge_request.rb

@@ -189,7 +189,7 @@ class MergeRequest < ActiveRecord::Base
       self.merge!(current_user.id)
       true
     end
-  rescue 
+  rescue
     self.mark_as_unmergable
     false
   end

app/models/project/repository_trait.rb

@@ -114,5 +114,9 @@ module Project::RepositoryTrait
     def root_ref 
       default_branch || "master"
     end
+
+    def root_ref? branch
+      root_ref == branch
+    end
   end
 end