Activity functions throw an ArgumentNullException when they don't return a value

[bachuv]

Summary: Not returning a value in an activity function throws an ArgumentNullException saying Value cannot be null. (Parameter: input). Durable Functions docs state that activity functions can optionally return a value (https://learn.microsoft.com/en-us/azure/azure-functions/durable/quickstart-powershell-vscode#create-your-functions).

Repro:

This code throws the exception

param($name)

Write-Host "Hello $name!" 

This code works as expected

param($name)

"Hello $name!" 

Workaround:
Return a non-null value from the activity function.