When all member roles are "locked" not possible to set default role for new members

[jcogs-design]

Description of the problem
Not sure if this is a bug or a feature ... but if a CP user sets all of the member roles to be "Security Locked" then EE does not make it possible to assign a "default role" to new members (as the list of possible roles to assign to the member is blank).

Unclear what is set in the slot for "default role" in exp_members if this happens.

Environment Details:

• Version: 7.4.11
• PHP Version 7.4

Possible Solution
Unclear why 'locked' roles cannot be assigned to the 'default role' option.

[intoeetive]

The docs state this:

Security Lock -- If enabled, only Super Admin users can add or remove members to the role.

So the locked role cannot be used as default, because using locked role required superadmin intervention

@ExpressionEngine/expressionengine-dev-team I keep this ticket open so someone could update the docs accordingly, giving more information about the expected behavior

[jcogs-design]

I understand what the docs say.
What is not clear is what happens when no default role can be assigned to a member.
What role to they get? Or do they get none? If so how does EE work out what they have permission to do?
Or is it not possible to create new members while all are locked down?