ActiveJob: allow blank queue names

As discussed in #17195, Que uses blank queue names by default for
performance reasons. At the very least, ActiveJob should allow users to
choose "" as their queue name. This commit allows blank queue names, as
well as tests to make sure that nil queue names still use the default.

activejob/lib/active_job/queue_name.rb

@@ -24,7 +24,7 @@ def queue_as(part_name=nil, &block)
       end
 
       def queue_name_from_part(part_name) #:nodoc:
-        queue_name = part_name.to_s.presence || default_queue_name
+        queue_name = part_name || default_queue_name
         name_parts = [queue_name_prefix.presence, queue_name]
         name_parts.compact.join('_')
       end

activejob/test/cases/queue_naming_test.rb

@@ -18,6 +18,26 @@ class QueueNamingTest < ActiveSupport::TestCase
     end
   end
 
+  test 'allows a blank queue name' do
+    begin
+      original_queue_name = HelloJob.queue_name
+      HelloJob.queue_as ""
+      assert_equal "", HelloJob.new.queue_name
+    ensure
+      HelloJob.queue_name = original_queue_name
+    end
+  end
+
+  test 'does not use a nil queue name' do
+    begin
+      original_queue_name = HelloJob.queue_name
+      HelloJob.queue_as nil
+      assert_equal "default", HelloJob.new.queue_name
+    ensure
+      HelloJob.queue_name = original_queue_name
+    end
+  end
+
   test 'evals block given to queue_as to determine queue' do
     begin
       original_queue_name = HelloJob.queue_name