Steps to Reproduce

1. run the attached example
2. click "notify" button

Current Result

zk.wpd:26252 Uncaught TypeError: Cannot read property 'value' of undefined
at init.bind_ (zul.inp.wpd:828)
at init.$supers (zk.wpd:12819)
at init.bind_ (zul.db.wpd:1143)
at init.bindChildren_ (zk.wpd:22520)
at init.bind_ (zk.wpd:22483)
at init.$supers (zk.wpd:12819)
at init.bind_ (zul.inp.wpd:825)
at init.$supers (zk.wpd:12819)
at init.bind_ (zul.db.wpd:3366)
at init.bindChildren_ (zk.wpd:22520)

Expected Result

no error.

Debug Information

• textbox, intbox, and spinner don't have this bug.