possible null reference

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11107 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c
Issue 6820:	java.lang.IllegalArgumentException: No enum constant org.primefaces.model.SortOrder.1

git-svn-id: http://primefaces.googlecode.com/svn/primefaces/trunk@11109 5a70e874-a5cb-11dd-8af2-493fb0bb9f7c