Licences External ID field is not mandatory

[mudesmi]

Description

System Admin > Licences External ID field is not mandatory.

LIcence should not get created without External ID. Creating licence with no external id gives below error.And licence list in the Licence Management 

06:24:58.434 [http-apr-13401-exec-7] ERROR org.finos.waltz.web.Main - Generic Exception: externalId / java.lang.NullPointerException
java.lang.NullPointerException: externalId

Waltz Version

1.68

Steps to Reproduce

1.Navigate to System Admin > Licences.
2.Create Licence without External ID.

Expected Result

Save button should be disabled if external Id field is empty.

Actual Result

Save button is enabled when external Id field is empty.