• but need to deal with SQL function _nullIf() param type mismatch

sql_gen.py code to use:

class RawLiteral(Code):
    def __init__(self, value):
        Code.__init__(self)

        self.value = value

    def to_str(self, db): return db.esc_value(self.value)

class Literal(RawLiteral):
    def to_str(self, db):
        if util.is_str(self.value): # avoid text literals having type `unknown`
            return Cast('text', RawLiteral(self.value)).to_str(db)
        return RawLiteral.to_str(self, db)