[TD-2302]<fix>: fix nodejs exception when query a null value

src/connector/nodejs/test/testNull.js

@@ -0,0 +1,10 @@
+const taos = require('../tdengine');
+var conn = taos.connect({host: "127.0.0.1", user: "root", password: "taosdata", config: "/etc/taos", port: 6030});
+var c1 = conn.cursor();
+
+
+c1.query('select * from test.weather', true).then(function (result) {
+    result.pretty();
+});
+
+conn.close();