Issue with ~Mu

[coke]

S03-operators/context-forcers.t expects this test to pass:

niecza> dies_ok { ~Mu }
not ok 2
# (eval) line 1

But it only warns:

niecza> ~ Mu
Use of uninitialized value in string context
  at /home/coke/sandbox/niecza/lib/CORE.setting line 1388 (warn @ 5)
  at /home/coke/sandbox/niecza/lib/CORE.setting line 269 (Mu.Str @ 15)
  at <unknown> line 0 (ExitRunloop @ 0)
  at (eval) line 1 (mainline @ 2)
  at <unknown> line 0 (ExitRunloop @ 0)

[moritz]

FWIW it is correct that that ~Mu only warns. The question is whether dies_ok should treat warnings as errors; I'm not sure there's an unambiguous decision on that in the specs.