Prevent undefined method `<=>' for nil:NilClass in AbstractAdapter (#4098).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2957 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/scm/adapters/abstract_adapter.rb

@@ -215,7 +215,7 @@ module Redmine
         def sort_by_name
           sort {|x,y| 
             if x.kind == y.kind
-              x.name <=> y.name
+              x.name.to_s <=> y.name.to_s
             else
               x.kind <=> y.kind
             end