Guard against null phone number value
Guard against null phone number value

"parsePhoneNumber()" expects a string, so a TypeError would be thrown if
the phone number value is null.

Signed-off-by: Daniel Calviño Sánchez <bd7629e975cc0e00ea7cda4ab6a120f2ee42ac1b@gmail.com>

nextcloud/server,nextcloud/server,nextcloud/server,nextcloud/server