use in vue,first is ok ,then error error

[Clearives]

handleLogin: function() {
      if (this.userid == '' || this.password == '') return;
      let params = {
        userid: this.userid,
        password: md5.update(this.password).digest('hex')
      };
      debugger;
    },

browser.js?7e92:19 Uncaught TypeError: Cannot read property 'push' of null
    at HashNoConstructor._update (eval at <anonymous> (0.3d0ebe5….hot-update.js:391), <anonymous>:19:15)
    at HashNoConstructor.CipherBase.update (eval at <anonymous> (0.3d0ebe5….hot-update.js:329), <anonymous>:21:22)
    at VueComponent.handleLogin (eval at <anonymous> (0.3d0ebe5….hot-update.js:6), <anonymous>:30:23)
    at boundFn (eval at <anonymous> (app.js:717), <anonymous>:165:14)
    at VueComponent.invoker (eval at <anonymous> (app.js:717), <anonymous>:1738:18)
    at VueComponent.Vue.$emit (eval at <anonymous> (app.js:717), <anonymous>:2207:16)
    at VueComponent.handleClick (eval at <anonymous> (app.js:2976), <anonymous>:1256:12)
    at boundFn (eval at <anonymous> (app.js:717), <anonymous>:165:14)
    at HTMLButtonElement.invoker (eval at <anonymous> (app.js:717), <anonymous>:1738:18)