check for unset vars

git-svn-id: https://plugins.svn.wordpress.org/wpbook-lite/trunk@967386 b8457f37-d9ea-0310-8a92-e5e31aec5664
check for unset vars

git-svn-id: https://plugins.svn.wordpress.org/wpbook-lite/trunk@967388 b8457f37-d9ea-0310-8a92-e5e31aec5664
check unset vars

git-svn-id: https://plugins.svn.wordpress.org/wpbook-lite/trunk@967391 b8457f37-d9ea-0310-8a92-e5e31aec5664