App-vNext/Polly · error · ArgumentNullException

Value cannot be null. (Parameter 'ttlStrategy')

Error message

Value cannot be null. (Parameter 'ttlStrategy')

What it means

Thrown by the terminal CacheAsync<TResult>(...) overload when ttlStrategy is null. The TTL strategy decides how long cached values live; a null strategy would leave expiration undefined, so construction is rejected. The provider guard runs first, so this only fires when the provider is valid but the TTL is null.

Solutions

1. Pass a concrete ITtlStrategy<TResult> such as new RelativeTtl(TimeSpan.FromMinutes(5)).
2. If you only need a fixed TTL, prefer the TimeSpan-based overload which constructs RelativeTtl for you.
3. Null-check the strategy at the call site.

Example fix

// before
var policy = Policy.CacheAsync<string>(provider, (ITtlStrategy<string>)null, keyFunc, onGet, onMiss, onPut, null, null);
// after
var policy = Policy.CacheAsync<string>(provider, new RelativeTtl(TimeSpan.FromMinutes(5)).For<string>(), keyFunc, onGet, onMiss, onPut, null, null);

var ttl = ttlStrategy ?? new RelativeTtl(TimeSpan.FromMinutes(5));
var policy = Policy.CacheAsync<TResult>(provider, ttl.For<TResult>(), keyFunc, onGet, onMiss, onPut, null, null);

static bool HasTtl<T>(ITtlStrategy<T>? s) => s is not null;

try { var p = Policy.CacheAsync<R>(provider, ttl, keyFunc, onGet, onMiss, onPut, null, null); }
catch (ArgumentNullException ex) when (ex.ParamName == "ttlStrategy") { /* default the TTL or fail */ }

When it happens

Trigger: Calling the full overload (or a public overload that funnels here) with a null ITtlStrategy<TResult>, e.g. passing null where a RelativeTtl or ContextualTtl should be.

Common situations: The TTL strategy field was never assigned; a config-driven TTL factory returned null when the config section was absent; refactor swapped in an overload that no longer wraps TimeSpan into RelativeTtl.

Related errors

• Value cannot be null. (Parameter 'action')
• Value cannot be null. (Parameter 'onCacheGet')
• Value cannot be null. (Parameter 'onCacheMiss')
• Value cannot be null. (Parameter 'onCachePut')
• Value cannot be null. (Parameter 'wrappedCacheProvider')

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/057c499d0eb7028d. Report an issue: GitHub.

Appendix: source

Thrown at src/Polly/Caching/AsyncCacheTResultSyntax.cs:986

    /// <exception cref="ArgumentNullException">Thrown when <paramref name="onCachePut"/> is <see langword="null"/>.</exception>
    public static AsyncCachePolicy<TResult> CacheAsync<TResult>(
        IAsyncCacheProvider<TResult> cacheProvider,
        ITtlStrategy<TResult> ttlStrategy,
        Func<Context, string> cacheKeyStrategy,
        Action<Context, string> onCacheGet,
        Action<Context, string> onCacheMiss,
        Action<Context, string> onCachePut,
        Action<Context, string, Exception>? onCacheGetError,
        Action<Context, string, Exception>? onCachePutError)
    {
        if (cacheProvider == null)
        {
            throw new ArgumentNullException(nameof(cacheProvider));
        }

        if (ttlStrategy == null)
        {
            throw new ArgumentNullException(nameof(ttlStrategy));
        }

        if (cacheKeyStrategy == null)
        {
            throw new ArgumentNullException(nameof(cacheKeyStrategy));
        }

        if (onCacheGet == null)
        {
            throw new ArgumentNullException(nameof(onCacheGet));
        }

        if (onCacheMiss == null)
        {
            throw new ArgumentNullException(nameof(onCacheMiss));
        }

        if (onCachePut == null)

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