message: use PrimVal::is_null
diff: @@ -892,7 +892,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  }
  pub(super) fn pointer_offset(&self, ptr: PrimVal, pointee_ty: Ty<'tcx>, offset: i64) -> EvalResult<'tcx, PrimVal> {
  - if ptr == PrimVal::from_u128(0) { // rule out NULL pointers
  + if ptr.is_null()? { // rule out NULL pointers
  return Err(EvalError::InvalidPointerMath);
  }
  // FIXME: assuming here that type size is < i64::max_value()
  