Bug 18361: [QA Follow-up] Resolve warning on undef values supplied

Bug 18361: [QA Follow-up] Resolve warning on undef values supplied

The following warning was raised in Letters.t:
DBIx::Class::ResultSource::_minimal_valueset_satisfying_constraint():
NULL/undef values supplied for requested unique constraint 'primary' (NULL
values in column(s): 'id'). This is almost certainly not what you wanted,
though you can set DBIC_NULLABLE_KEY_NOWARN to disable this warning.

This warning is triggered by this line in C4/Letters.pm:
    Koha::SMS::Providers->find( $member->{'sms_provider_id'} );
As you already guessed, the sms_provider_id returns undef.

Resolved in sub find by testing if there are parameters and if so, they
should not be all undefined. (In most cases there will be only one
parameter; but this report is about composite keys.)

Added a trivial test case in Objects.t too.

Test plan:
Run t/db_dependent/Koha/Object.t
Run t/db_dependent/Koha/Objects.t
Run t/db_dependent/Letters.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>