Clicking on add condition while trying to create a metric threshold alert doesn't do anything on UI

[bhavyarm]

Kibana version: 7.7.0 BC6

Elasticsearch version: 7.7.0 BC6

Server OS version: cloud

Browser version: Chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): on cloud deployment

Describe the bug: When user tries to create a metric threshold alert and clicks on add condition - nothing happens and Kibana has "kbn-ui-shared-deps.js:342 Uncaught TypeError: Cannot read property 'slice' of undefined" in console

Steps to reproduce:

1. Get 7.7.0 BC6 up on cloud in production, install sample data and navigate to alerts and actions in under management
2. Click on create alert - select metric threshold and fill in data for name, tags (optional) and time interval details
3. Try to click on add condition -nothing happens
   and Kibana logs

kbn-ui-shared-deps.js:342 Uncaught TypeError: Cannot read property 'slice' of undefined
    at infra.plugin.js:17
    at Object.m (kbn-ui-shared-deps.js:342)
    at w (kbn-ui-shared-deps.js:342)
    at kbn-ui-shared-deps.js:342
    at x (kbn-ui-shared-deps.js:342)
    at L (kbn-ui-shared-deps.js:342)
    at T (kbn-ui-shared-deps.js:342)
    at O (kbn-ui-shared-deps.js:342)
    at Cn (kbn-ui-shared-deps.js:342)
    at ce (kbn-ui-shared-deps.js:342)
(anonymous) @ infra.plugin.js:17
m @ kbn-ui-shared-deps.js:342
w @ kbn-ui-shared-deps.js:342
(anonymous) @ kbn-ui-shared-deps.js:342
x @ kbn-ui-shared-deps.js:342
L @ kbn-ui-shared-deps.js:342
T @ kbn-ui-shared-deps.js:342
O @ kbn-ui-shared-deps.js:342
Cn @ kbn-ui-shared-deps.js:342
ce @ kbn-ui-shared-deps.js:342
Ln @ kbn-ui-shared-deps.js:342
Dn @ kbn-ui-shared-deps.js:342
On @ kbn-ui-shared-deps.js:342
t.unstable_runWithPriority @ kbn-ui-shared-deps.js:350
Hi @ kbn-ui-shared-deps.js:342
se @ kbn-ui-shared-deps.js:342
Tn @ kbn-ui-shared-deps.js:342

Expected behavior: Should be able to create alerts?

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[phillipb]

This is a known issue and should be fixed by #63514 in the RC.