Allow and skip null handlers when adding a vararg list of handlers
Motivation
Allowing null handlers allows for more convenient idioms in
conditionally adding handlers, e.g.,
ch.pipeline().addLast(
new FooHandler(),
condition ? new BarHandler() : null,
new BazHandler()
);
Modifications
* Change addFirst(..) and addLast(..) to skip null handlers, rather than
break or short-circuit.
* Add new unit tests.
Result
* Makes addFirst(..) and addLast(..) behavior more consistent
* Resolves https://github.com/netty/netty/issues/10728
5a725edf4a