UI mat-select components should not have empty lists
In the UI there are certain cases where the mat-select options are only present when another form control satisfies some condition. This results in a mat-select with an empty list. Clicking on such an element gives no feedback to the user and can be misinterpreted as a broken form element. I would suggest that when there are no options in the select list, to provide a single disabled item with some text letting the user know that there are no options available.
One good example is the Certificate field in Directory Services/ LDAP
FYI: The implementation for this is commented out in the form-select html template.