Fix implementation of GetValueOrCreateAsync in NullMemcachedClient

Author: cnblogs-dudu

Enyim.Caching/Enyim.Caching.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <Description>EnyimMemcachedCore is a Memcached client library for .NET Core. Usage: Add services.AddEnyimMemcached(...) and app.UseEnyimMemcached() in Startup. Add IMemcachedClient into constructor.</Description>
-    <VersionPrefix>2.1.0.3</VersionPrefix>
+    <VersionPrefix>2.1.0.4</VersionPrefix>
     <Authors>cnblogs.com</Authors>
     <TargetFramework>netstandard2.0</TargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

Enyim.Caching/NullMemcachedClient.cs

@@ -250,7 +250,7 @@ public Task SetAsync(string key, object value, int cacheSeconds)
 
         public Task<T> GetValueOrCreateAsync<T>(string key, int cacheSeconds, Func<Task<T>> factory)
         {
-            return Task.FromResult(default(T));
+            return factory();
         }
     }
 }