Claiming trimmed messages from a stream leads to an error

[flash-gordon]

What happens:

1. Consumer reads a message then fails.
2. The message is added to the list of pending.
3. After a while, the stream is trimmed and the message is removed yet it's still on the list of pending.
4. Recover process tries to claim the message, redis-rb throws an error;

redis.xclaim(stream, consumer_group, consumer, 0, [pending_id])

       undefined method `each_slice' for nil:NilClass
     # redis-4.2.1/lib/redis.rb:3428:in `block (2 levels) in <class:Redis>'
     # redis-4.2.1/lib/redis.rb:3427:in `map'
     # redis-4.2.1/lib/redis.rb:3427:in `block in <class:Redis>'
     # redis-4.2.1/lib/redis/client.rb:130:in `call'
     # redis-4.2.1/lib/redis.rb:3222:in `block in xclaim'
     # redis-4.2.1/lib/redis.rb:69:in `block in synchronize'
     # /Users/gordon/.rvm/rubies/ruby-2.7.1/lib/ruby/2.7.0/monitor.rb:202:in `synchronize'
     # /Users/gordon/.rvm/rubies/ruby-2.7.1/lib/ruby/2.7.0/monitor.rb:202:in `mon_synchronize'
     # redis-4.2.1/lib/redis.rb:69:in `synchronize'
     # redis-4.2.1/lib/redis.rb:3222:in `xclaim'

I think trimmed messages should result in nil.

[flash-gordon]

There's justid option in xclaim that will avoid hashifying fetched records. Still, the current error is confusing, it'd be better to have MessageDeletedError or something like that.

[supercaracal]

It seems like that the error is related to #929.