App-vNext/Polly · error · ArgumentNullException

onRetryAsync

Error message

onRetryAsync

What it means

Thrown by RetryAsync<TResult> when the async callback Func<DelegateResult<TResult>, int, Task> onRetryAsync is null. This overload forwards to the context-aware variant with a discarded context; it only null-checks onRetryAsync and delegates retryCount validation downstream. The callback is invoked and awaited on each retry, so null is rejected at construction.

Source

Thrown at src/Polly/Retry/AsyncRetryTResultSyntax.cs:92

#pragma warning restore 1998
    }

    /// <summary>
    ///     Builds an <see cref="AsyncRetryPolicy{TResult}" /> that will retry <paramref name="retryCount" /> times
    ///     calling <paramref name="onRetryAsync" /> on each retry with the handled exception or result and retry count.
    /// </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="onRetryAsync">The action to call asynchronously 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="onRetryAsync"/> is <see langword="null"/>.</exception>
    public static AsyncRetryPolicy<TResult> RetryAsync<TResult>(this PolicyBuilder<TResult> policyBuilder, int retryCount, Func<DelegateResult<TResult>, int, Task> onRetryAsync)
    {
        if (onRetryAsync == null)
        {
            throw new ArgumentNullException(nameof(onRetryAsync));
        }

        return policyBuilder.RetryAsync(retryCount, onRetryAsync: (outcome, i, _) => onRetryAsync(outcome, i));
    }

    /// <summary>
    /// Builds an <see cref="AsyncRetryPolicy{TResult}"/> that will retry once
    /// calling <paramref name="onRetry"/> on retry with the handled exception or result, retry count and context data.
    /// </summary>
    /// <typeparam name="TResult">The type of the result.</typeparam>
    /// <param name="policyBuilder">The policy builder.</param>
    /// <param name="onRetry">The action to call on each retry.</param>
    /// <returns>The policy instance.</returns>
    /// <exception cref="ArgumentNullException">Thrown when <paramref name="onRetry"/> is <see langword="null"/>.</exception>
    public static AsyncRetryPolicy<TResult> RetryAsync<TResult>(this PolicyBuilder<TResult> policyBuilder, Action<DelegateResult<TResult>, int, Context> onRetry) =>
        policyBuilder.RetryAsync(1, onRetry);

    /// <summary>

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Pass a non-null Func<DelegateResult<TResult>, int, Task>.
2. Coalesce the optional argument: onRetryAsync ?? NoOpRetryAsync.
3. Pick a parameterless-onRetry overload if no hook is required.

Example fix

// before
.RetryAsync(3, onRetryAsync: null);
// after
.RetryAsync(3, onRetryAsync: async (outcome, i) => await Log.RetryAsync(outcome, i));

if (onRetryAsync is null) throw new InvalidOperationException("onRetryAsync required.");
// then call RetryAsync<TResult>(retryCount, onRetryAsync)

static bool IsValidOnRetry(Func<DelegateResult<TResult>, int, Task> f) => f is not null;

try { Policy.HandleResult<T>(IsHandled).RetryAsync(retryCount, onRetryAsync); }
catch (ArgumentNullException ex) when (ex.ParamName == nameof(onRetryAsync))
{ /* supply a completed-task no-op callback */ }

When it happens

Trigger: Calling RetryAsync<TResult>(retryCount, onRetryAsync: null), or accepting an optional Func from a wrapper and passing it through unguarded.

Common situations: Wrapper that exposes an optional async retry hook, or DI resolving the callback as null.

Related errors

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

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/6e7c86b648a379e7. Report an issue: GitHub.