Negation of type checks

[hastebrot]

To negate type checks I currently have to use t.refinement():

t.refinement(t.Nil, value => !t.Nil.is(value), "NotNil")(null)

Would it make sense to add a t.negate() to refine type checkers with negation?

t.NotNil = t.negate(t.Nil, "NotNil")
t.NotNil(null)