Add abilityto add oneself to lists (#12271)

* Add ability to add oneself to lists

* Change search results to include oneself when searching through followers

* Mark follow relation as optional in ListAccount

app/models/list_account.rb

@@ -6,13 +6,13 @@
 #  id         :bigint(8)        not null, primary key
 #  list_id    :bigint(8)        not null
 #  account_id :bigint(8)        not null
-#  follow_id  :bigint(8)        not null
+#  follow_id  :bigint(8)
 #
 
 class ListAccount < ApplicationRecord
   belongs_to :list
   belongs_to :account
-  belongs_to :follow
+  belongs_to :follow, optional: true
 
   validates :account_id, uniqueness: { scope: :list_id }
 
@@ -21,6 +21,6 @@ class ListAccount < ApplicationRecord
   private
 
   def set_follow
-    self.follow = Follow.find_by(account_id: list.account_id, target_account_id: account.id)
+    self.follow = Follow.find_by!(account_id: list.account_id, target_account_id: account.id) unless list.account_id == account.id
   end
 end