Add defensive check to GetRecurringJobIds to prevent null reference exception

[jshin-relativity]

In the HangfireWorkflowScheduler, it is possible for the GetRecurringJobIds method to throw a null reference exception, and I have observed this occurring when multiple instances have their triggers being updated after a workflow definition change at the same time, even with distributed locking set up in Elsa. I believe this will at least prevent the null reference exception; without this, the handler crashes and recurring jobs get left around.

Below is a snippet from the Hangfire code that retrieves the list

https://github.com/HangfireIO/Hangfire/blob/eb994c324c0ed2687e2c35412c72460a1c1f9e71/src/Hangfire.Core/Storage/StorageConnectionExtensions.cs#L75

        public static List<RecurringJobDto> GetRecurringJobs([NotNull] this IStorageConnection connection)
        {
            if (connection == null) throw new ArgumentNullException(nameof(connection));

            var ids = connection.GetAllItemsFromSet("recurring-jobs");
            return GetRecurringJobDtos(connection, ids);
        }

And the GetRecurringJobDtos method can definitely return objects without a Job set.

https://github.com/HangfireIO/Hangfire/blob/eb994c324c0ed2687e2c35412c72460a1c1f9e71/src/Hangfire.Core/Storage/StorageConnectionExtensions.cs#L89

        private static List<RecurringJobDto> GetRecurringJobDtos(IStorageConnection connection, IEnumerable<string> ids)
        {
            var result = new List<RecurringJobDto>();
            foreach (var id in ids)
            {
                var hash = connection.GetAllEntriesFromHash($"recurring-job:{id}");

                // TODO: Remove this in 2.0 (breaking change)
                if (hash == null)
                {
                    result.Add(new RecurringJobDto { Id = id, Removed = true });
                    continue;
                }

                var dto = new RecurringJobDto { Id = id };

                if (hash.TryGetValue("Cron", out var cron) && !String.IsNullOrWhiteSpace(cron))
                {
                    dto.Cron = cron;
                }

                try
                {
                    if (hash.TryGetValue("Job", out var payload) && !String.IsNullOrWhiteSpace(payload))
                    {
                        var invocationData = InvocationData.DeserializePayload(payload);
                        dto.Job = invocationData.DeserializeJob();
                    }
                }
                catch (JobLoadException ex)
                {
                    dto.LoadException = ex;
                }

[greptile-apps]

Greptile Overview

Greptile Summary

Added defensive null check to GetRecurringJobIds method to prevent NullReferenceException in race conditions when multiple instances update workflow triggers simultaneously.

• The pattern check x.Job is { Args.Count: > 0 } ensures both Job and Args are non-null before accessing Args[0]
• Prevents crashes during concurrent job cleanup when distributed locking doesn't fully prevent race conditions
• Maintains existing filtering logic while making it more resilient to edge cases

Confidence Score: 4/5

• This PR is safe to merge with minimal risk
• The defensive null check is a targeted fix addressing a real production issue without changing behavior for valid cases. The pattern matching syntax correctly validates both Job and Args existence before array access.
• No files require special attention

Important Files Changed

Filename	Overview
src/modules/scheduling/Elsa.Scheduling.Hangfire/Services/HangfireWorkflowScheduler.cs	Added null-safety check to prevent NullReferenceException when accessing job arguments in concurrent scenarios

[jshin-relativity]

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