`Repo.exists` can't use `nil` as it is unsafe.
Use parent object instead of activity because currently Announce activity's context is null.
false <- Pleroma.Web.ActivityPub.MRF.subdomain_match?(domain_blocks, item_host),
false <- Pleroma.Web.ActivityPub.MRF.subdomain_match?(domain_blocks, parent_host),
true <- thread_containment(item, user),
- false <- CommonAPI.thread_muted?(user, item) do
+ false <- CommonAPI.thread_muted?(user, parent) do
false
else
_ -> true