I am working on a new plugin which uses this call.  Based on experience with another plugin's return values from hooks, I am thinking that the only return values from this function should be either null or true.  There is one case where false is returned which conflicts with the plugin I am working on which was set to return true in similar cases.

I can change mine but I am just verifying what is supposed to be correct.

I just realized - I am one of those who still uses 3.2.0.  However, 4.0.5 has the same 'issue.'

The return does'nt matter, being true or false. Anything "not null" does cancel the later functions after the hook position.

Sure.  This is more about convention or standardization, I suppose:

18:01 [Warning] Calling hook OnOvenToggle resulted in a conflict between the following plugins: QuickSmelt - False (Boolean), MyPlugin (True (Boolean))