"fall-through" generic function args plus &context

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I have a few defmethods that use the &context construct to dispatch on
the value of major mode:

(cl-defmethod my-make-buffer-name (&context (major-mode gnus-summary-mode))
  ;; etc...
  )

I need a catch-all method, for default behavior when we're in other
modes that aren't targeted by an existing method.

I've tried things like:

(&context _major-mode)
(&context (major-mode t))
(&context (major-mode nil))
(&context (major-mode (eql _nuthin))

And a few other things. Everything raises cl-no-applicable-method.

What's the correct way to do this? Or do I need to override
`cl-no-applicable-method' and catch the error?

Thanks,
Eric