Bio can actually be nil.

lib/pleroma/web/ostatus/ostatus.ex

@@ -162,7 +162,7 @@ defmodule Pleroma.Web.OStatus do
 
     with false <- user.local,
          avatar <- make_avatar_object(doc),
-         bio when not is_nil(bio) <- string_from_xpath("//author[1]/summary", doc),
+         bio <- string_from_xpath("//author[1]/summary", doc),
          name when not is_nil(name) <- string_from_xpath("//author[1]/poco:displayName", doc),
          new_data <- %{avatar: avatar, name: name, bio: bio},
          false <- new_data == old_data do