[ICE] Empty data type causes `EmitCore` crash

[Y-Nak]

Summary

Defining an empty data type (a type with no constructors, analogous to Haskell's Void) and using it as an arg/return type causes an ICE in EmitCore.hs. The compiler crashes with "empty sum" error when trying to translate the type.

Minimal Reproduction

data Void;

function todo() -> Void {
    assembly {
        revert(0, 0)
    }
}

contract C {
    function main()  {
        todo();
    }
}

↓

ERROR: empty sum Void
in: function signature function todo () -> Void
in: function todo

sol-core: Emit core failed
CallStack (from HasCallStack):
  error, called at src/Solcore/Desugarer/EmitCore.hs:38:3 in sol-core-0.0.0.0-inplace:Solcore.Desugarer.EmitCore
  errorsEM, called at src/Solcore/Desugarer/EmitCore.hs:214:25 in sol-core-0.0.0.0-inplace:Solcore.Desugarer.EmitCore

TODO: We also probably need to discuss the typing rule for the empty(or bottom) type.