diff --git a/lib/gitlab/project_search_results.rb b/lib/gitlab/project_search_results.rb
index 581a8c20bdb85e2275d8fe6dbf14cd0424a104b1..0dab7bcfa4d0c9af1081042fdd3121bdb924b779 100644
--- a/lib/gitlab/project_search_results.rb
+++ b/lib/gitlab/project_search_results.rb
@@ -4,7 +4,11 @@ module Gitlab
 
     def initialize(project_id, query, repository_ref = nil)
       @project = Project.find(project_id)
-      @repository_ref = repository_ref
+      @repository_ref = if repository_ref.present?
+                          repository_ref
+                        else
+                          nil
+                        end
       @query = Shellwords.shellescape(query) if query.present?
     end