Internal Comment tab throws a JAVA Script error

There is a JAVA Script error in the Internal Comment tab of Service Desk interface:

Uncaught TypeError: Cannot read property 'indexOf' of undefined
a
(anonymous function)
d.event.dispatchbatch
d.event.add.g.handle.i

Steps to reproduce.

1. Open a Google Chrome browser session, or any other browser with JAVA Console.
2. Create a Service Desk.
3. Create a request.
4. Open the request in the Service Desk interface.
5. Click in the comment field, then select the Internal Comment tab with the JAVA Console opened.