App-vNext/Polly · error · ArgumentNullException

Value cannot be null. (Parameter 'cacheKeyStrategy')

Error message

Value cannot be null. (Parameter 'cacheKeyStrategy')

What it means

Thrown by the 8-parameter typed-result overload CacheAsync<TResult>(IAsyncCacheProvider cacheProvider, TimeSpan ttl, ICacheKeyStrategy cacheKeyStrategy, Action onCacheGet, ...) (AsyncCacheTResultSyntax.cs:261) when cacheKeyStrategy is null. The strategy is dereferenced for cacheKeyStrategy.GetCacheKey, so a null instance NREs and is therefore guarded.

Source

Thrown at src/Polly/Caching/AsyncCacheTResultSyntax.cs:278

    /// <exception cref="ArgumentNullException">Thrown when <paramref name="onCachePut"/> is <see langword="null"/>.</exception>
    public static AsyncCachePolicy<TResult> CacheAsync<TResult>(
        IAsyncCacheProvider cacheProvider,
        TimeSpan ttl,
        ICacheKeyStrategy 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 (cacheKeyStrategy is null)
        {
            throw new ArgumentNullException(nameof(cacheKeyStrategy));
        }

        return CacheAsync(cacheProvider.AsyncFor<TResult>(), new RelativeTtl(ttl), cacheKeyStrategy.GetCacheKey, onCacheGet, onCacheMiss, onCachePut, onCacheGetError, onCachePutError);
    }

    /// <summary>
    /// <para>Builds an <see cref="AsyncPolicy{TResult}" /> that will function like a result cache for delegate executions returning a <typeparamref name="TResult"/>.</para>
    /// <para>Before executing a delegate, checks whether the <paramref name="cacheProvider" /> holds a value for the cache key determined by applying the <paramref name="cacheKeyStrategy"/> to the execution <see cref="Context"/>.
    /// If the <paramref name="cacheProvider" /> provides a value from cache, returns that value and does not execute the governed delegate.  If the <paramref name="cacheProvider" /> does not provide a value, executes the governed delegate, stores the value with the <paramref name="cacheProvider" />, then returns the value.
    /// </para>
    /// </summary>
    /// <typeparam name="TResult">The type of the result.</typeparam>
    /// <param name="cacheProvider">The cache provider.</param>
    /// <param name="ttlStrategy">A strategy for specifying ttl for values to be cached.</param>
    /// <param name="cacheKeyStrategy">The cache key strategy.</param>
    /// <param name="onCacheGet">Delegate to call on a cache hit, when value is returned from cache.</param>
    /// <param name="onCacheMiss">Delegate to call on a cache miss.</param>
    /// <param name="onCachePut">Delegate to call on cache put.</param>

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Pass a non-null ICacheKeyStrategy instance.
2. Use DefaultCacheKeyStrategy via an overload that omits the strategy argument if OperationKey suffices.

Example fix

// before
Policy.CacheAsync<MyResult>(provider, TimeSpan.FromMinutes(5), (ICacheKeyStrategy)null, onGet, onMiss, onPut, onGetErr, onPutErr);

// after
Policy.CacheAsync<MyResult>(provider, TimeSpan.FromMinutes(5), new MyKeyStrategy(), onGet, onMiss, onPut, onGetErr, onPutErr);

if (cacheKeyStrategy is null) throw new InvalidOperationException("cacheKeyStrategy must be provided.");
var policy = Policy.CacheAsync<TResult>(cacheProvider, TimeSpan.FromMinutes(5), cacheKeyStrategy, onGet, onMiss, onPut, onGetErr, onPutErr);

static bool IsKeyStrategyValid(ICacheKeyStrategy? s) => s is not null;

When it happens

Trigger: Calling Policy.CacheAsync<TResult>(cacheProvider, TimeSpan.FromMinutes(5), (ICacheKeyStrategy)null, onCacheGet, onCacheMiss, onCachePut, onCacheGetError, onCachePutError).

Common situations: Switching to a custom key strategy but not instantiating it; the strategy DI registration missing.

Related errors

• Value cannot be null.
• Value cannot be null. (Parameter 'cacheProvider')
• onRetry
• sleepDurationProvider
• Value cannot be null. (Parameter 'ttlStrategy')

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/588f6767f5ffd59f. Report an issue: GitHub.