Issuable#labels_with_details can raise an error if a label was deleted
We fixed https://gitlab.com/gitlab-org/gitlab-triage/issues/141 but another error can happen:
gitlab-triage-2ff786d82126/lib/gitlab/triage/resource/shared/issuable.rb:31:in `uniq': undefined method `name' for nil:NilClass (NoMethodError)
from gitlab-triage-2ff786d82126/lib/gitlab/triage/resource/shared/issuable.rb:31:in `labels_with_details'
So we should ignore those labels. They're not useful anyway.