bug#47925: 28.0.50; define-minor-mode without body results in false warning

[Jonas Bernoulli]

I have a mode that leaves out all the optional arguments because its
sole purpose is the enable its minor-mode map:

  (define-minor-mode transient-resume-mode
    "Auxiliary minor-mode used to resume a transient after viewing help.")

which is supported:

  (define-minor-mode MODE DOC [KEYWORD VAL ... &rest BODY])

Unfortunately that results in a warning:

  transient.el:3318:20: Warning: Use keywords rather than deprecated positional
      arguments to `define-minor-mode'

because INIT-VALUE is nil in this case, not keywordp.