The manual, chapter 3, contains the following phrase for command handlers that return nothing:
As return value in such a case, you are recommended to use
Void.TYPE, the official representation of the
I find it weird to recommend returning a reference of type java.lang.Class. The value referred to by Void.TYPE is the class object that represents void, it is not something of type Void (nor void) itself.
I would recommend returning null, the only value of type java.lang.Void.