reject non-string. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@26071 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test for r25067. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25935 b2dd03c8-39d4-4d8f-98ff-823fe69b080e