Person.find_or_fetch_by_identifier never return nil

Person.find_or_fetch_by_identifier raises an exception if person is not found localy and not fetchable. It never returns nil. These code changes take care about this behaviour and changes specs and code to behave equally.

Also related to #8253

app/models/user.rb

@@ -442,8 +442,13 @@ class User < ApplicationRecord
     aq = self.aspects.create(:name => I18n.t('aspects.seed.acquaintances'))
 
     if AppConfig.settings.autofollow_on_join?
-      default_account = Person.find_or_fetch_by_identifier(AppConfig.settings.autofollow_on_join_user)
-      self.share_with(default_account, aq) if default_account
+      begin
+        default_account = Person.find_or_fetch_by_identifier(AppConfig.settings.autofollow_on_join_user)
+        share_with(default_account, aq)
+      rescue DiasporaFederation::Discovery::DiscoveryError
+        logger.warn "Error auto-sharing with #{AppConfig.settings.autofollow_on_join_user}
+                     fix autofollow_on_join_user in configuration."
+      end
     end
     aq
   end

app/workers/fetch_webfinger.rb

@@ -12,7 +12,9 @@ module Workers
       person = Person.find_or_fetch_by_identifier(account)
 
       # also, schedule to fetch a few public posts from that person
-      Diaspora::Fetcher::Public.queue_for(person) unless person.nil?
+      Diaspora::Fetcher::Public.queue_for(person)
+    rescue DiasporaFederation::Discovery::DiscoveryError
+      # Ignored
     end
   end
 end

spec/models/user_spec.rb

@@ -811,10 +811,10 @@ describe User, :type => :model do
       context "with autofollow sharing enabled" do
         it "should start sharing with autofollow account" do
           AppConfig.settings.autofollow_on_join = true
-          AppConfig.settings.autofollow_on_join_user = "one"
-
-          expect(Person).to receive(:find_or_fetch_by_identifier).with("one")
+          person = FactoryBot.build(:person)
+          AppConfig.settings.autofollow_on_join_user = person.diaspora_handle
 
+          expect(Person).to receive(:find_or_fetch_by_identifier).with(person.diaspora_handle).and_return(person)
           user.seed_aspects
         end
       end

spec/workers/fetch_webfinger_spec.rb

@@ -11,7 +11,7 @@ describe Workers::FetchWebfinger do
   end
 
   it "should webfinger and queue no job to fetch public posts if the person is not found" do
-    allow(Person).to receive(:find_or_fetch_by_identifier).and_return(nil)
+    allow(Person).to receive(:find_or_fetch_by_identifier).and_raise DiasporaFederation::Discovery::DiscoveryError
 
     expect(Diaspora::Fetcher::Public).not_to receive(:queue_for)