App-vNext/Polly · error · ArgumentNullException

onRetry

Error message

onRetry

What it means

This generic Retry<TResult> overload (RetryTResultSyntax.cs:59) throws ArgumentNullException when onRetry is null. The callback Action<DelegateResult<TResult>, int> reports each retry's handled result/exception and attempt number; it is mandatory.

Source

Thrown at src/Polly/Retry/RetryTResultSyntax.cs:59

    /// calling <paramref name="onRetry"/> 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="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="onRetry"/> is <see langword="null"/>.</exception>
    public static RetryPolicy<TResult> Retry<TResult>(this PolicyBuilder<TResult> policyBuilder, int retryCount, Action<DelegateResult<TResult>, int> onRetry)
    {
        if (retryCount < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(retryCount), "Value must be greater than or equal to zero.");
        }

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

        return policyBuilder.Retry(retryCount, (outcome, i, _) => onRetry(outcome, i));
    }

    /// <summary>
    /// Builds a <see cref="Policy{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 RetryPolicy<TResult> Retry<TResult>(this PolicyBuilder<TResult> policyBuilder, Action<DelegateResult<TResult>, int, Context> onRetry) =>
        policyBuilder.Retry(1, onRetry);

    /// <summary>

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Pass a non-null Action<DelegateResult<TResult>, int>.
2. If no callback is wanted, use the Retry(int) overload that omits onRetry.

Example fix

// before
var policy = Policy.HandleResult<int>(r => r < 0).Retry(3, null);
// after
var policy = Policy.HandleResult<int>(r => r < 0).Retry(3, (outcome, attempt) => log.LogWarning("retry {Attempt}", attempt));

if (onRetry is null) throw new ArgumentNullException(nameof(onRetry));
var policy = Policy.HandleResult<int>(r => r < 0).Retry(3, onRetry);

When it happens

Trigger: Calling Policy.HandleResult<T>(...).Retry(retryCount, null) with onRetry typed Action<DelegateResult<TResult>, int>.

Common situations: Removed logging; field null; overload-resolution confusion with the Context-bearing variant.

Related errors

• sleepDurations
• Value must be greater than or equal to zero.
• onRetry
• onRetryAsync
• 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/5757f8b6c7c65b94. Report an issue: GitHub.