rspec/rules/S4586/vbnet/rule.adoc

:keyword_null: Nothing
:keyword_async: Async
:concept_method: procedure
:typeparameter_TResult: (Of TResult)

== Why is this an issue?

include::../why-dotnet.adoc[]

[source,vbnet]
----
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

include::../how-to-fix-it-dotnet.adoc[]

=== Code examples

A `Task` returning {concept_method} can be fixed like so:

==== Noncompliant code example

[source,vbnet,diff-id=1,diff-type=noncompliant]
----
Public Function DoFooAsync() As Task
    Return Nothing            ' Noncompliant: Causes a NullReferenceException if awaited.
End Function
----

==== Compliant solution

[source,vbnet,diff-id=1,diff-type=compliant]
----
Public Function DoFooAsync() As Task
    Return Task.CompletedTask ' Compliant: Method can be awaited.
End Function
----

A `Task{typeparameter_TResult}` returning {concept_method} can be fixed like so:

==== Noncompliant code example

[source,vbnet,diff-id=2,diff-type=noncompliant]
----
Public Function GetFooAsync() As Task(Of Object)
    Return Nothing                             ' Noncompliant: Causes a NullReferenceException if awaited.
End Function
----

==== Compliant solution

[source,vbnet,diff-id=2,diff-type=compliant]
----
Public Function GetFooAsync() As Task(Of Object)
    Return Task.FromResult(Of Object)(Nothing) ' Compliant: Method can be awaited.
End Function
----

include::../resources.adoc[]

include::../rspecator.adoc[]