Reworked code as part of fix

gistfile1.txt

/*
Nuget packages included:
    - AzureFromTheTrenches.Commanding 6.1.0
    - AzureFromTheTrenches.Commanding.MicrosoftDependencyInjection 6.1.0
    - Microsoft.Extensions.DependencyInjection 2.0.0
*/

using System;
using System.Threading.Tasks;
using AzureFromTheTrenches.Commanding;
using AzureFromTheTrenches.Commanding.Abstractions;
using Microsoft.Extensions.DependencyInjection;

namespace CommandingTest
{
    class Program
    {
        static void Main(string[] args)
        {
            IServiceProvider serviceProvider = null;
            var serviceCollection = new ServiceCollection();
            var registry = CommandingDependencies.UseCommanding(
                new CommandingDependencyResolver(
                    (type, instance) => serviceCollection.AddSingleton(type, instance),
                    (type, impl) => serviceCollection.AddTransient(type, impl),
                    type => serviceProvider.GetService(type)
                )
            );
            registry.Register<TestCommandHandler>();
            serviceProvider = serviceCollection.BuildServiceProvider();
            var commandDispatcher = serviceProvider.GetService<ICommandDispatcher>();
            commandDispatcher.DispatchAsync(new TestCommand()).Wait();
        }
    }

    class TestCommand : ICommand
    {
        public int Param { get; set; }
    }

    class TestCommandHandler : ICommandHandler<TestCommand>
    {
        public Task ExecuteAsync(TestCommand command)
        {
            throw new ApplicationException("This should be thrown!");
        }
    }
}