Should the undefined be accepted as the value of Listbox component with multiple?

[ronny1020]

This issue is based on the following PR.
#2295

In my opinion, since the option will be undefined before it is selected without a default value, particularly when it comes to an optional field, although the problem can be solved by passing an empty array, I believe it would be more convenient for users to allow undefined.

If it is determined that undefined should not be allowed in a normal case, I think it should also be prevented from being used in the typescript type.

To be honest, I just got a bug about opening a list box without a default value. and I took a lot of time to figure out what had happened.