crucible-syntax: Poor error message on program with uninitialized register

[RyanGlScott]

This program crashes with a rather confusing error message:

(defun @test () Unit
  (registers
    ($i Bool))

  (start start:
    (assert! (equal? $i $i) "Assertion")
    (return ())))

$ cabal run crucibler -- check test.cbl 
Up to date
crucibler: Input block type [BoolRepr] does not match expected []:
while SSA converting function test
CallStack (from HasCallStack):
  error, called at src/Lang/Crucible/CFG/SSAConversion.hs:976:24 in crucible-0.6-inplace:Lang.Crucible.CFG.SSAConversion

It seems like the semantics of registers are such that they have to be initialized before they can be used, as the error message goes away if an intervening (set-register! $i ...) statement is added. If so, the error message should say as much.