def test_untyped(self):
        """test conversion of null, empty string"""
        conn = self.connect()
        c = conn.cursor()
        c.execute("select null,''")
        self.assertEqual((None, ""), c.fetchone())
        c.execute("select '',null")
        self.assertEqual(("", None), c.fetchone())
test conversion of null, empty string
pymysql/tests/test_basic.py