Putting a wrong watch can hang the Watcher UI

[spinscale]

Kibana version: 7.6.1
Elasticsearch version: 7.6.1
Server OS version: osx
Browser version: brave
Browser OS version: osx
Original install method (e.g. download page, yum, from source, etc.): download tar.gz

Description of the problem including expected versus actual behavior:

Steps to reproduce:

1. Go to Management > Elasticsearch > Watcher
2. Create new advanced watch
3. Copy this snippet into the textbox

{
  "trigger": {
    "schedule": {
      "interval": "5m"
    }
  },
  "input": {
    "simple": {
      "foo": "bar"
    }
  },
  "actions": {
    "log": {
      "logging": {
        "text": {
          "inline": ""
        }
      }
    }
  }
}

5. Click create watch and wait for eternity

Errors in browser console (if relevant):

Detected an unhandled Promise rejection.
TypeError: Cannot read property 'data' of undefined
51.bundle.js:3 Uncaught (in promise) TypeError: Cannot read property 'data' of undefined
    at saveWatch$ (51.bundle.js:3)
    at s (kbn-ui-shared-deps.js:338)
    at Generator._invoke (kbn-ui-shared-deps.js:338)
    at Generator.forEach.e.<computed> [as throw] (kbn-ui-shared-deps.js:338)
    at s (kbn-ui-shared-deps.js:338)
    at t (kbn-ui-shared-deps.js:338)
    at kbn-ui-shared-deps.js:338

Animated GIF of the issue...

[cjcenizal]

Thanks @spinscale! I was able to verify this on master.

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)