Unmet conditions not propagated when a guard prevents a transition

[Ninho67]

We have recently done 2 things in our code base:

• use FireAsync instead of Fire
• moved from Stateless 5.16.0 to 5.20.1

Our unit tests suddenly started failing because the unmet conditions were not present in the StatelessTransitionException<,> exception anymore.
Rolling back to 5.17.0 works. Tests start failing in 5.18.0.

I haven't checked the code in details, but have noticed this in debug:

        private async Task InternalFireOneAsync(TTrigger trigger, params object[] args)
        {
            if (_triggerConfiguration.TryGetValue(trigger, out TriggerWithParameters configuration))
            {
                configuration.ValidateParameters(args);
            }

            var source = State;
            var representativeState = GetRepresentation(source);

            var foundHandler = await representativeState.TryFindHandlerAsync(trigger, args);

            if (foundHandler == null || foundHandler.UnmetGuardConditions.Any())
            {
                await _unhandledTriggerAction.ExecuteAsync(representativeState.UnderlyingState, trigger, null); // <|----
                return;
            }

In the code above, we're entering the last if condition with foundHandler not null but with 1 unmet guard. In the next line, null is passed for unmet guards. Could this be a bug ?

Thanks in advance for your answer