Raise if MemCacheStore doenst receive a Dalli obj

:mem_cache_store should receive a list of hosts or a dalli client,
otherwise raise it.
Also adding a changelog.

activesupport/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   MemCacheStore should only accept a Dalli::Client, or create one.
+
+    *arthurnn*
+
 *   Don't lazy load the `tzinfo` library as it causes problems on Windows.
 
     Fixes #13553

activesupport/lib/active_support/cache/mem_cache_store.rb

@@ -46,6 +46,9 @@ module ActiveSupport
         options = addresses.extract_options!
         super(options)
 
+        unless [String, Dalli::Client, NilClass].include?(addresses.first.class)
+          raise ArgumentError, "First argument must be an empty array, an array of hosts or a Dalli::Client instance."
+        end
         if addresses.first.is_a?(Dalli::Client)
           @data = addresses.first
         else

activesupport/test/caching_test.rb

@@ -110,6 +110,14 @@ class CacheStoreSettingTest < ActiveSupport::TestCase
     assert_kind_of(ActiveSupport::Cache::MemCacheStore, store)
   end
 
+  def test_mem_cache_fragment_cache_store_with_not_dalli_client
+    Dalli::Client.expects(:new).never
+    memcache = Object.new
+    assert_raises(ArgumentError) do
+      ActiveSupport::Cache.lookup_store :mem_cache_store, memcache
+    end
+  end
+
   def test_mem_cache_fragment_cache_store_with_multiple_servers
     Dalli::Client.expects(:new).with(%w[localhost 192.168.1.1], {})
     store = ActiveSupport::Cache.lookup_store :mem_cache_store, "localhost", '192.168.1.1'