Redis cache store: fix expanding empty keys with no namespace

activesupport/lib/active_support/cache/redis_cache_store.rb

@@ -444,11 +444,11 @@ module ActiveSupport
 
         # Truncate keys that exceed 1kB.
         def normalize_key(key, options)
-          truncate_key super.b
+          truncate_key super&.b
         end
 
         def truncate_key(key)
-          if key.bytesize > max_key_bytesize
+          if key && key.bytesize > max_key_bytesize
             suffix = ":sha2:#{::Digest::SHA2.hexdigest(key)}"
             truncate_at = max_key_bytesize - suffix.bytesize
             "#{key.byteslice(0, truncate_at)}#{suffix}"

activesupport/test/cache/behaviors/cache_store_behavior.rb

@@ -110,6 +110,12 @@ module CacheStoreBehavior
     end
   end
 
+  def test_read_multi_with_empty_keys_and_a_logger_and_no_namespace
+    @cache.options[:namespace] = nil
+    @cache.logger = ActiveSupport::Logger.new(nil)
+    assert_equal({}, @cache.read_multi)
+  end
+
   def test_fetch_multi
     @cache.write("foo", "bar")
     @cache.write("fud", "biz")