It helps to get a stack trace when debugging issues. Certain things are
considered bugs in the code (like missing attributes in a struct), and
might cause a panic in certain occasions.
In this case, a missing string will not panic, but the behaviour will
also not be correct (DEKs getting encrypted, but unable to decrypt).
Clearly logging this as a BUG is probably better than calling panic().
Signed-off-by: Niels de Vos <ndevos@redhat.com>