CRR0031 - The returned Task is null

• May 06, 2018

This analyzer detects the asynchronous methods that return null. A Task-typed method returning null may appear after refactoring and causes the NullReferenceException when the method is called with the await keyword.

C#

Task<string> DemoMethodAsync(CancellationToken token) {
    DoThings();
    return null;
}

VB.NET

Private Function DemoMethodAsync(token As CancellationToken) As Task(Of String)
    DoThings()
    Return Nothing
End Function

You should construct a Task from null and return it to fix this issue.

C#

Task<string> DemoMethodAsync(CancellationToken token) {
    DoThings();
    return Task.FromResult<string>(null);
}

VB.NET

Private Function DemoMethodAsync(ByVal token As CancellationToken) As Task(Of String)
    DoThings()
    Return Task.FromResult(Of String)(Nothing)
End Function