Task return type gives not all code paths return a value

Question

I have a method implemented from an interface which looks as follows..

public Task CreateAsync(ApplicationUser user)
{
     if (user == null)
     {
         throw new ArgumentNullException("user");
     }
     Task.Factory.StartNew(() => { Console.WriteLine("Hello Task library!"); }); 
     //I even tried
     //Task.Run(() => { Console.WriteLine("Hello Task library!"); });

}

The above code gives me an error not all code paths return a value.

Answer 1

returning Task.CompletedTask is cleaner.

public Task CreateAsync(ApplicationUser user)
{
  if (user == null)
  {
     throw new ArgumentNullException("user");
  }

   Task.Factory.StartNew(() => { Console.WriteLine("Hello Task library!"); }); 
   // other operations

   return Task.CompletedTask;
 }

Answer 2

Needs a return :

 return Task.Factory.StartNew(() => { Console.WriteLine("Hello Task library!"); });

Or better:

return Task.Run(() => { Console.WriteLine("Hello Task library!"); });