Exclude non existent repository storages.

db/migrate/20161220141214_remove_dot_git_from_group_names.rb

@@ -61,7 +61,7 @@ class RemoveDotGitFromGroupNames < ActiveRecord::Migration
   def move_namespace(group_id, path_was, path)
     repository_storage_paths = select_all("SELECT distinct(repository_storage) FROM projects WHERE namespace_id = #{group_id}").map do |row|
       Gitlab.config.repositories.storages[row['repository_storage']]
-    end
+    end.compact
     # Move the namespace directory in all storages paths used by member projects
     repository_storage_paths.each do |repository_storage_path|