Best way to handle null task inside async method? [closed]

Question

What is the best way to handle a null task inside an async method?

public class MyClass
{
   private readonly Task task;
   public MyClass(Task task) { this.task = task; }

   public async Task Execute()
   {
      if (task == null)
      {
         await Task.Yield(); /* Is this the best way? */
         return;
      }
      await task;
   }
}

Answer 1

You don't need to handle null tasks. Simply null check it:

public async Task Execute()
{
   if (task != null)
   {
       await task;
   }
}

Or even better, simply return the task since you're not adding anything after the await:

public Task Execute()
{
   return task;
}

If you want to return a completed task instead of null you can use Task.FromResult:

public Task Execute()
{
   return task ?? Task.FromResult(false);
}

Answer 2

Most asynchronous code is cleaner if tasks are never null. Instead of a null task, use Task.FromResult(0) or some such construct.

public class MyClass
{
  private readonly Task task;
  public MyClass(Task task) { this.task = task ?? Task.FromResult(0); }

  public async Task ExecuteAsync()
  {
    await task;
  }
}

Or, if that's really all your ExecuteAsync is doing:

public Task ExecuteAsync()
{
  return task;
}

Note that the task is already running when the constructor is called, which makes the method name ExecuteAsync a misnomer. If you want the task to start when ExecuteAsync is called, then what you really want to store is a Func<Task>:

public class MyClass
{
  private readonly Func<Task> func;
  public MyClass(Func<Task> func) { this.func = func ?? () => Task.FromResult(0); }

  public async Task ExecuteAsync()
  {
    await func();
  }
}