App-vNext/Polly · error · ArgumentNullException

sleepDurationProvider

Error message

sleepDurationProvider

What it means

ArgumentNullException thrown at construction by the 4-argument WaitAndRetry<TResult>(retryCount, Func<int,DelegateResult<TResult>,Context,TimeSpan> sleepDurationProvider, Action<...> onRetry) when sleepDurationProvider is null. The provider is invoked per attempt to compute the wait, so a null value would throw later during execution; Polly validates it eagerly with parameter name 'sleepDurationProvider'.

Source

Thrown at src/Polly/Retry/RetryTResultSyntax.cs:285

    /// </summary>
    /// <typeparam name="TResult">The type of the result.</typeparam>
    /// <param name="policyBuilder">The policy builder.</param>
    /// <param name="retryCount">The retry count.</param>
    /// <param name="sleepDurationProvider">The function that provides the duration to wait for a particular retry attempt.</param>
    /// <param name="onRetry">The action to call on each retry.</param>
    /// <returns>The policy instance.</returns>
    /// <exception cref="ArgumentOutOfRangeException">retryCount;Value must be greater than or equal to zero.</exception>
    /// <exception cref="ArgumentNullException">Thrown when <paramref name="sleepDurationProvider"/> or <paramref name="onRetry"/> is <see langword="null"/>.</exception>
    public static RetryPolicy<TResult> WaitAndRetry<TResult>(this PolicyBuilder<TResult> policyBuilder, int retryCount, Func<int, TimeSpan> sleepDurationProvider, Action<DelegateResult<TResult>, TimeSpan, int, Context> onRetry)
    {
        if (retryCount < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(retryCount), "Value must be greater than or equal to zero.");
        }

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

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

        var sleepDurations = Enumerable.Range(1, retryCount)
                                       .Select(sleepDurationProvider);

        return new RetryPolicy<TResult>(
            policyBuilder,
            onRetry,
            retryCount,
            sleepDurationsEnumerable: sleepDurations);
    }

    /// <summary>

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Supply a provider such as n => TimeSpan.FromSeconds(n) or a backoff function.
2. Use a simpler WaitAndRetry overload (fixed TimeSpan list) if dynamic durations are not needed.
3. Pass an existing provider instance variable confirmed non-null.

Example fix

// before
var p = Policy.HandleResult<int>(r => r == 0).WaitAndRetry(3, null, onRetry);

// after
var p = Policy.HandleResult<int>(r => r == 0)
    .WaitAndRetry(3, (attempt, outcome, ctx) => Backoff.Decorate(attempt), onRetry);

if (sleepDurationProvider == null) throw new InvalidOperationException("sleepDurationProvider required.");
var policy = Policy.HandleResult<T>(pred).WaitAndRetry(retryCount, sleepDurationProvider, onRetry);

static bool IsProvider<TResult>(Func<int, DelegateResult<TResult>, Context, TimeSpan> p) => p is not null;

When it happens

Trigger: Calling policyBuilder.WaitAndRetry<TResult>(retryCount, null, onRetry) where the second argument (the context-aware provider) is null. Also when a Func field wired from config is null.

Common situations: Developer wired onRetry but forgot to supply the duration provider; a DI-registered provider type failed to resolve; refactor changed the provider signature and left a null.

Related errors

• sleepDurations
• Value cannot be null.
• Value cannot be null.
• Value must be greater than zero.
• Value must be greater than or equal to zero.

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/000e9f98ba4fc564. Report an issue: GitHub.