David Turner 77dd711847 Tidy up GroupedActionListener (#39633)
Today the `GroupedActionListener` accepts a `defaults` parameter but all
callers pass an empty list. Also it is permitted to pass an empty group but
this is trappy because the delegated listener is never be called in that case.
This commit removes the `defaults` parameter and forbids an empty group.
2019-03-06 09:25:10 +00:00
..