Allow ActivityPub Note's tag and attachment to be single objects (#5534)

app/helpers/jsonld_helper.rb

@@ -9,6 +9,10 @@ module JsonLdHelper
     value.is_a?(Array) ? value.first : value
   end
 
+  def as_array(value)
+    value.is_a?(Array) ? value : [value]
+  end
+
   def value_or_id(value)
     value.is_a?(String) || value.nil? ? value : value['id']
   end

app/lib/activitypub/activity/create.rb

@@ -53,9 +53,9 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   end
 
   def process_tags(status)
-    return unless @object['tag'].is_a?(Array)
+    return if @object['tag'].nil?
 
-    @object['tag'].each do |tag|
+    as_array(@object['tag']).each do |tag|
       case tag['type']
       when 'Hashtag'
         process_hashtag tag, status
@@ -103,9 +103,9 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   end
 
   def process_attachments(status)
-    return unless @object['attachment'].is_a?(Array)
+    return if @object['attachment'].nil?
 
-    @object['attachment'].each do |attachment|
+    as_array(@object['attachment']).each do |attachment|
       next if unsupported_media_type?(attachment['mediaType']) || attachment['url'].blank?
 
       href             = Addressable::URI.parse(attachment['url']).normalize.to_s