assert false; causes "Cannot read property 'replace' of undefined

Eh... don't think this is quite right... it seems an assert  without an ":" argument is not handled properly in the assert logging code.

Wed Oct 18 12:35:36 GMT-400 2017 com.google.gwt.logging.client.LogConfiguration
SEVERE: (TypeError) : Cannot read property 'replace' of undefined
com.google.gwt.core.client.JavaScriptException: (TypeError) : Cannot read property 'replace' of undefined