Merge pull request #22194 from grosser/grosser/read-nil

cache nil replies from backend cache so misses are fast too

activesupport/lib/active_support/cache/strategy/local_cache.rb

@@ -48,6 +48,10 @@ module ActiveSupport
             @data.clear
           end
 
+          def fetch(*args, &block)
+            @data.fetch(*args, &block)
+          end
+
           def read_entry(key, options)
             @data[key]
           end
@@ -99,12 +103,11 @@ module ActiveSupport
         protected
           def read_entry(key, options) # :nodoc:
             if local_cache
-              entry = local_cache.read_entry(key, options)
-              unless entry
+              local_cache.fetch(key) do
                 entry = super
                 local_cache.write_entry(key, entry, options)
+                entry
               end
-              entry
             else
               super
             end

activesupport/test/caching_test.rb

@@ -625,6 +625,14 @@ module LocalCacheBehavior
     end
   end
 
+  def test_local_cache_of_read_nil
+    @cache.with_local_cache do
+      assert_equal nil, @cache.read('foo')
+      @cache.send(:bypass_local_cache) { @cache.write 'foo', 'bar' }
+      assert_equal nil, @cache.read('foo')
+    end
+  end
+
   def test_local_cache_of_write_nil
     @cache.with_local_cache do
       assert @cache.write('foo', nil)