App-vNext/Polly · error · ArgumentNullException

onRetryAsync

Error message

onRetryAsync

What it means

ArgumentNullException is thrown when onRetryAsync is null in WaitAndRetryAsync(IEnumerable<TimeSpan> sleepDurations, Func<Exception,TimeSpan,Context,Task> onRetryAsync). This is the async counterpart of error 205 and wraps into the full 4-parameter delegate.

Source

Thrown at src/Polly/Retry/AsyncRetrySyntax.cs:784

#pragma warning restore 1998
    }

    /// <summary>
    ///     Builds an <see cref="AsyncRetryPolicy" /> that will wait and retry as many times as there are provided
    ///     <paramref name="sleepDurations" />
    ///     calling <paramref name="onRetryAsync" /> on each retry with the raised exception, the current sleep duration and context data.
    ///     On each retry, the duration to wait is the current <paramref name="sleepDurations" /> item.
    /// </summary>
    /// <param name="policyBuilder">The policy builder.</param>
    /// <param name="sleepDurations">The sleep durations to wait for on each retry.</param>
    /// <param name="onRetryAsync">The action to call asynchronously on each retry.</param>
    /// <returns>The policy instance.</returns>
    /// <exception cref="ArgumentNullException">Thrown when <paramref name="sleepDurations"/> or <paramref name="onRetryAsync"/> is <see langword="null"/>.</exception>
    public static AsyncRetryPolicy WaitAndRetryAsync(this PolicyBuilder policyBuilder, IEnumerable<TimeSpan> sleepDurations, Func<Exception, TimeSpan, Context, Task> onRetryAsync)
    {
        if (onRetryAsync == null)
        {
            throw new ArgumentNullException(nameof(onRetryAsync));
        }

        return policyBuilder.WaitAndRetryAsync(
            sleepDurations,
            onRetryAsync: (outcome, timespan, _, ctx) => onRetryAsync(outcome, timespan, ctx));
    }

    /// <summary>
    ///     Builds an <see cref="AsyncRetryPolicy" /> that will wait and retry as many times as there are provided
    ///     <paramref name="sleepDurations" />
    ///     calling <paramref name="onRetry" /> on each retry with the raised exception, the current sleep duration, retry count, and context data.
    ///     On each retry, the duration to wait is the current <paramref name="sleepDurations" /> item.
    /// </summary>
    /// <param name="policyBuilder">The policy builder.</param>
    /// <param name="sleepDurations">The sleep durations to wait for on each retry.</param>
    /// <param name="onRetry">The action to call on each retry.</param>
    /// <returns>The policy instance.</returns>
    /// <exception cref="ArgumentNullException">Thrown when <paramref name="sleepDurations"/> or <paramref name="onRetry"/> is <see langword="null"/>.</exception>

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Provide a Task-returning lambda accepting Context.
2. Use the overload without callback if none is needed.
3. Use a no-op default: (ex, delay, ctx) => Task.CompletedTask.

Example fix

// before
.WaitAndRetryAsync(durations, null)

// after
.WaitAndRetryAsync(durations, (ex, delay, ctx) =>
{
    logger.LogWarning("Retry {Id} after {Delay}", ctx.OperationKey, delay);
    return Task.CompletedTask;
})

if (onRetryAsync is null)
    onRetryAsync = (_, _, _) => Task.CompletedTask;

static bool IsValidCallback(Func<Exception, TimeSpan, Context, Task> cb) => cb is not null;

When it happens

Trigger: Calling this overload with a null async callback delegate that includes Context.

Common situations: DI registration that did not bind the callback, or a refactor that removed the callback while keeping the overload choice.

Related errors

• onRetry
• sleepDurations
• sleepDurationProvider
• sleepDurations
• 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/7f8d2e164d92b6a4. Report an issue: GitHub.