Implement assurance that facility for clearing fetched values from password
password-protected items when the password is removed, so inadvertent leaks
can be prevented on reuse of the itmes.

Use this facility in Public ShareRoom models.
Affirm that removing a public share room password clears the fetched
values.

(The crucial assertion requires confirming that an attribute has the
undefined value, which cannot be done directly with the changed .should.
So I'm using chai.expect(value).to.equal(undefined) - I think this is the
right way to do it.)