Move status serializer error handling to private method (#29031)

app/controllers/api/v1/statuses_controller.rb

@@ -73,11 +73,7 @@ class Api::V1::StatusesController < Api::BaseController
 
     render json: @status, serializer: serializer_for_status
   rescue PostStatusService::UnexpectedMentionsError => e
-    unexpected_accounts = ActiveModel::Serializer::CollectionSerializer.new(
-      e.accounts,
-      serializer: REST::AccountSerializer
-    )
-    render json: { error: e.message, unexpected_accounts: unexpected_accounts }, status: 422
+    render json: unexpected_accounts_error_json(e), status: 422
   end
 
   def update
@@ -159,6 +155,17 @@ class Api::V1::StatusesController < Api::BaseController
     @status.is_a?(ScheduledStatus) ? REST::ScheduledStatusSerializer : REST::StatusSerializer
   end
 
+  def unexpected_accounts_error_json(error)
+    {
+      error: error.message,
+      unexpected_accounts: serialized_accounts(error.accounts),
+    }
+  end
+
+  def serialized_accounts(accounts)
+    ActiveModel::Serializer::CollectionSerializer.new(accounts, serializer: REST::AccountSerializer)
+  end
+
   def pagination_params(core_params)
     params.slice(:limit).permit(:limit).merge(core_params)
   end