Added check for null value
Fixed chosen sellect all, sellect none functionality when multiple instances on page

git-svn-id: https://plugins.svn.wordpress.org/advanced-custom-fields-categories/trunk@745951 b8457f37-d9ea-0310-8a92-e5e31aec5664
recommit

git-svn-id: https://plugins.svn.wordpress.org/advanced-custom-fields-categories/trunk@745952 b8457f37-d9ea-0310-8a92-e5e31aec5664