Why is this an issue?
Returning Nothing from a non-Async Task/Task(Of TResult) procedure will cause a
NullReferenceException at runtime if the procedure is awaited. This problem can be avoided by returning Task.CompletedTask or Task.FromResult(Of TResult)(Nothing)
respectively.
Public Function DoFooAsync() As Task
Return Nothing ' Noncompliant: Causes a NullReferenceException if awaited.
End Function
Public Async Function Main() As Task
Await DoFooAsync() ' NullReferenceException
End Function
How to fix it
Instead of Nothing Task.CompletedTask or Task.FromResult(Of TResult)(Nothing)
should be returned.
Code examples
A Task returning procedure can be fixed like so:
Noncompliant code example
Public Function DoFooAsync() As Task
Return Nothing ' Noncompliant: Causes a NullReferenceException if awaited.
End Function
Compliant solution
Public Function DoFooAsync() As Task
Return Task.CompletedTask ' Compliant: Method can be awaited.
End Function
A Task(Of TResult) returning procedure can be fixed like so:
Noncompliant code example
Public Function GetFooAsync() As Task(Of Object)
Return Nothing ' Noncompliant: Causes a NullReferenceException if awaited.
End Function
Compliant solution
Public Function GetFooAsync() As Task(Of Object)
Return Task.FromResult(Of Object)(Nothing) ' Compliant: Method can be awaited.
End Function
Resources
Documentation
Articles & blog posts
