RE: Add Nullif case for eval_const_expressions_mutator

> +                if (!has_nonconst_input)
> +                    return ece_evaluate_expr(expr);
>
> That's not okay without a further check to see if the comparison function used
> by the node is immutable.  Compare ScalarArrayOpExpr, for instance.

Thanks for pointing it out.
Attaching new patch with this change.

Best regards,
houzj