Fix exception caused by adding a nil representation of a tree node.
Fix exception caused by adding a nil representation of a tree node.

chenbk85/sequelpro,chenbk85/sequelpro,chenbk85/sequelpro,CoolSwitcher/sequelpro,dnl-jst/sequelpro,abhibeckert/sequelpro,dnl-jst/sequelpro,Jellyfrog/sequelpro,josegonzalez/sequelpro,kaneshin/sequelpro,treejames/sequelpro,kaneshin/sequelpro,leichunxin/sequelpro,Jellyfrog/sequelpro,treejames/sequelpro,CoolSwitcher/sequelpro,CoolSwitcher/sequelpro,treejames/sequelpro,eric-seekas/sequelpro,chenbk85/sequelpro,josegonzalez/sequelpro,abhibeckert/sequelpro,eric-seekas/sequelpro,eric-seekas/sequelpro,leichunxin/sequelpro,kaneshin/sequelpro,eric-seekas/sequelpro,Jellyfrog/sequelpro,CoolSwitcher/sequelpro,abhibeckert/sequelpro,kaneshin/sequelpro,josegonzalez/sequelpro,leichunxin/sequelpro,josegonzalez/sequelpro,dnl-jst/sequelpro,Jellyfrog/sequelpro,dnl-jst/sequelpro,abhibeckert/sequelpro,leichunxin/sequelpro,treejames/sequelpro