IRedisDatabase.GetAsync<T> used with Value Type returns default when key not found

[jirihalaska]

Describe the bug
IRedisDatabase.GetAsync<T> states that it returns T? (nullable) and null if not present. But when I use it with a value type (int, bool), the method actually returns default of that value type when called like this:

IRedisDatabase.GetAsync<int> returns 0 (I would expect null)
IRedisDatabase.GetAsync<int?> returns null correctly

This contradicts the documentation of the method

To Reproduce

• Setup redis in a Docker container from https://github.com/redis/redis/archive/refs/tags/8.0.3.tar.gz. Based on Alpine Linux.
• Configure connection to Redis as follows:

var redisConfig = new RedisConfiguration
{
      AbortOnConnectFail = false,
      ConnectionString = redisConnectionString,
      AllowAdmin = true,
      ConnectTimeout = 3000,
      SyncTimeout = 2000,
      Database = 0,
      Ssl = true,
      PoolSize = 5,
      IsDefault = true,
      Name = serviceName
};
var serializer = new SystemTextJsonSerializer(OrionJsonOptions.Default);

var redisClientFactory = new RedisClientFactory(redisConfig, loggerFactory, serializer);

var redisDatabase = redisClientFactory
    .GetDefaultRedisClient()
    .GetDefaultDatabase();

Following Calls should imho both return null

var badValue = await redisDatabase.GetAsync<int>("SomeKey"); // returns 0
var goodValue = await redisDatabase.GetAsync<int?>("SomeKey"); // returns null

Expected behavior
Both calls return null because the signature is
Task<T?> GetAsync<T>(string key, CommandFlags flag = CommandFlags.None);

Desktop (please complete the following information):

• OS: MacOS
• Runtime version .NET Core 9
• Version 8.0.3

Additional context

• So far I observed this behavior on MacOS

[CodersRealm]

Hi jirihalaska

This isn't a bug with GetAsync<T>. In fact, its behavior is desired when working with generics and value types. If T is a value type, then the return needs to be a value type because the compiler doesn't know how to convert a generic T value type to Nullable<T>. This behavior differs from that of reference types, which can be null.

Here is an example:

T? GetValue<T>()
{
    object? t = null;
    return (T?)t;
}

string? result1 = GetValue<string>();
int? result2 = GetValue<int>();

This code will compile and run, then blow up when calling the method with the generic type parameter int.

Cheers

[jirihalaska]

Thank you for your reply.

I do understand the implications of default of a value object. It is very easy to overlook this behavior and introduce bugs in my own code, though. From the developer's perspective, I wish there were a warning telling me that when I call IRedisDatabase.GetAsync<int>(), I should expect the default value 0, not null, when the item is not found. Even if I assign to int?.

[imperugo]

Hi @jirihalaska, thanks for the detailed report.

As @CodersRealm correctly explained, this is a C# language constraint rather than a bug in the library. When T is a value type (like int), T? does not become Nullable<T> — the compiler treats it as T itself. This means GetAsync<int>() can only return 0 (the default) when the key doesn't exist, not null.

The correct approach is to use GetAsync<int?>() when you need to distinguish between "key not found" and "value is 0".

I understand this can be surprising. I'll consider improving the XML documentation to make this behavior more explicit for value types in a future release.

Thanks for bringing this up!

[imperugo]

The fix for this issue is now available on NuGet in v12.0.0. You can upgrade with:

dotnet add package StackExchange.Redis.Extensions.Core --version 12.0.0

See the full release notes for all changes in this release. Thanks!