`GetNamedActivityPropertyAsync()` throws NRE when called on `CompositeActivity`

[ann-shakun]

Hi!

When using CompositeActivity it seems it's not possible to access activity output by calling GetNamedActivityPropertyAsync(). If you move A1 and A2 to the parent workflow, it works as expected. Am I missing something?

Reproduced in 2.4.1 and 2.5.0-preview.4.

public class TestWorkflow : IWorkflow
{
    public void Build(IWorkflowBuilder builder)
    {
        builder
            // any trigger
            .Then<A0>();
    }
}

public class A0 : CompositeActivity
{
    public override void Build(ICompositeActivityBuilder builder)
    {
        builder
            .Then<A1>().WithName(nameof(A1))
            .Then<A2>(s => s.Set(v => v.Input,
                async p => await p.GetNamedActivityPropertyAsync<A1, string>(nameof(A1),
                    a => a.Result)));
    }
}

public class A1 : Activity
{
    [ActivityOutput]
    public string Result { get; set; }

    protected override IActivityExecutionResult OnExecute()
    {
        Result = "test";
        return base.OnExecute();
    }
}

public class A2 : Activity
{
    [ActivityInput]
    public string Input
    {
        get => GetState<string>();
        set => SetState(value);
    }

    protected override IActivityExecutionResult OnExecute()
    {
        // do smth
        return base.OnExecute();
    }
}

Logs:

warn: Elsa.Services.Workflows.WorkflowRunner[0]
      Failed to run workflow 4baf2f5b63604b52864afad3daafaeb1
      Elsa.Exceptions.CannotSetActivityPropertyValueException: An exception was thrown whilst setting 'A2.Input'. See the inner exception for further details.
       ---> System.NullReferenceException: Object reference not set to an instance of an object.
         at Elsa.Services.Models.WorkflowExecutionContext.GetActivityPropertyAsync(IActivityBlueprint activityBlueprint, String propertyName, CancellationToken cancellationToken)
         at Elsa.Services.Models.WorkflowExecutionContext.GetNamedActivityPropertyAsync(String activityName, String propertyName, CancellationToken cancellationToken)
         at Elsa.Services.Models.WorkflowExecutionContext.GetNamedActivityPropertyAsync[T](String activityName, String propertyName, CancellationToken cancellationToken)
         at Elsa.Services.Models.WorkflowExecutionContext.GetNamedActivityPropertyAsync[TActivity,T](String activityName, Expression`1 propertyExpression, CancellationToken cancellationToken)
         at Elsa.Services.Models.ActivityExecutionContext.GetNamedActivityPropertyAsync[TActivity,T](String activityName, Expression`1 propertyExpression, CancellationToken cancellationToken)
         at ElsaWf.A0.<>c.<<Build>b__0_2>d.MoveNext() in <path>TestWorkflow.cs:line 28
      --- End of stack trace from previous location ---
         at Elsa.Builders.SetupActivity`1.<>c__DisplayClass6_0`1.<<Set>b__0>d.MoveNext()
      --- End of stack trace from previous location ---
         at Elsa.Services.Workflows.DelegateActivityPropertyValueProvider.GetValueAsync(ActivityExecutionContext context, CancellationToken cancellationToken)
         at Elsa.Services.ActivityPropertyProviders.SetActivityPropertiesAsync(IActivity activity, ActivityExecutionContext activityExecutionContext, CancellationToken cancellationToken)
         --- End of inner exception stack trace ---
         at Elsa.Services.ActivityPropertyProviders.SetActivityPropertiesAsync(IActivity activity, ActivityExecutionContext activityExecutionContext, CancellationToken cancellationToken)
         at Elsa.Services.Workflows.ActivityActivator.ActivateActivityAsync(ActivityExecutionContext context, Type type, CancellationToken cancellationToken)
         at Elsa.Providers.ActivityTypes.TypeBasedActivityProvider.<>c__DisplayClass6_0.<<CreateActivityTypeAsync>b__0>d.MoveNext()
      --- End of stack trace from previous location ---
         at Elsa.Services.Workflows.WorkflowRunner.RunCoreAsync(WorkflowExecutionContext workflowExecutionContext, ActivityOperation activityOperation, CancellationToken cancellationToken)
         at Elsa.Services.Workflows.WorkflowRunner.RunCoreAsync(WorkflowExecutionContext workflowExecutionContext, ActivityOperation activityOperation, CancellationToken cancellationToken)
         at Elsa.Services.Workflows.WorkflowRunner.RunAsync(WorkflowExecutionContext workflowExecutionContext, ActivityOperation activityOperation, CancellationToken cancellationToken)

[ann-shakun]

@sfmskywalker, I was looking into the source code and it seems like I found the reason of NRE.

https://github.com/elsa-workflows/elsa-core/blob/f3d64e3ac56198e1c73dd5212f2ec5b4b88d6c1c/src/core/Elsa.Abstractions/Services/Models/ActivityExecutionContext.cs#L252-L266

In my scenario container.Parent returned from GetCompositeName() is always null because A0 is inherited from CompositeActivity. Also valid for nested composite activities. So, instead of activity-1:A1 it returns A1. But I don't understand how to distinguish between named activity declared inside CompositeActivity and a CompositeActivity itself, because in both cases Parent is null.

[sfmskywalker]

Hi @ann-shakun , thanks for reporting this and the details you provided. We'll try and get this fixed for 2.5.1.