Handle empty list of types

[emteknetnz]

If there are no allowable types of links to be created the LinkPicker will end up with a fatal error e.g.

[Emergency] Uncaught InvalidArgumentException: "SilverStripe\LinkField\Form\LinkField": Allowed types cannot be empty

This can be forced with LinkField::create('MyLink')->setAllowedTypes([]);, though it's also possible if the CMS user fails canCreate() checks on the allowed link types.

Since the CMS user has no control over this, we should allow and empty list of types and display a UI message on the frontend instead of an empty dropdown

ACs

• There should be a message should be "Unable to create link"
• There should not be a fatal PHP error arriving via ajax
• If develop passes an empty array to setAllowedTypes() there should still be an exception because this is a developer error rather than a bunch of permission checks failing

PR

• ENH Show a cannot create message when types is empty #174

[GuySartorelli]

@emteknetnz Please add a link to the PR

[emteknetnz]

Done

[sabina-talipova]

PR was merged. Close.