Create subscription with `create_slot=false` and incorrect slot name

Hi

Maybe this question was already raised before, but I couldn't find a
discussion. When I'm creating a subscription with `create_slot=false` looks
like it's possible to pass a slot name with invalid characters. In this
particular case both publisher and subscriber were on the same machine:

=# CREATE SUBSCRIPTION test_sub CONNECTION 'dbname=db host=host
port=port user=user' PUBLICATION test_pub WITH (create_slot=false,
slot_name='test slot');
NOTICE: 00000: synchronized table states
LOCATION: CreateSubscription, subscriptioncmds.c:443
CREATE SUBSCRIPTION
Time: 5.887 ms

Of course `test slot` doesn't exist, because I can't create a slot with
incorrect name. And consequently I can't drop this subscription:

=# DROP SUBSCRIPTION test_sub;
ERROR: XX000: could not drop the replication slot "test slot" on
publisher
DETAIL: The error was: ERROR: replication slot name "test slot"
contains invalid character
HINT: Replication slot names may only contain lower case letters,
numbers, and the underscore character.
LOCATION: DropSubscription, subscriptioncmds.c:947
Time: 2.615 ms

=# CREATE SUBSCRIPTION test_sub CONNECTION 'dbname=db host=host
port=port user=user' PUBLICATION test_pub WITH (create_slot=false,
slot_name='test slot');
ERROR: 42710: subscription "test_sub" already exists
LOCATION: CreateSubscription, subscriptioncmds.c:344
Time: 0.492 ms

Is it an issue or I'm doing something wrong?