Cannot fetch posts on Concurrent

Environment

• Installation type (OTP or From Source): Source
• Pleroma version (could be found in the "Version" tab of settings in Pleroma-FE): 2.6.1
• Elixir version (elixir -v for from source installations, N/A for OTP): 1.14.5
• Operating system: FreeBSD 14.0-RELEASE-p3
• PostgreSQL version (psql -V): 16.1

Bug description

Pleroma cannot fetch posts which are on Concurrent (via ccworld-ap-bridge).

The following is the some messages left in the log file when I tried to fetch https://cc.mkdir.uk/ap/note/e5d1d0a1-1ab3-4498-9949-588e3fdea286:

pleroma[2945]: [error] Elixir.Pleroma.Web.MastodonAPI.SearchController search error: %Protocol.UndefinedError{protocol: Enumerable, value: nil, description: ""}
pleroma[2945]: [error] Error while fetching : {:error, "Unsupported URI scheme"}
pleroma[2945]: [warn] Couldn't fetch "", error: nil
pleroma[2945]: [error] Error while fetching : {:error, "Unsupported URI scheme"}
pleroma[2945]: [warn] Couldn't fetch "", error: nil
pleroma[2945]: [error] Error while fetching : {:error, "Unsupported URI scheme"}
pleroma[2945]: [warn] Couldn't fetch "", error: nil
pleroma[2945]: [error] Error while fetching : {:error, "Unsupported URI scheme"}
pleroma[2945]: [warn] Couldn't fetch "", error: nil
pleroma[2945]: [error] Elixir.Pleroma.Web.MastodonAPI.SearchController search error: %FunctionClauseError{module: Pleroma.Web.ActivityPub.ObjectValidators.CreateGenericValidator, function: :validate_context_match, arity: 2, kind: nil, args: nil, clauses: nil}

I couldn't judge if this is a problem on the Pleroma side or on the Concurrent side, but since I can fetch them on Misskey, I decided to create an issue here.