Known issues with runspaces

Exception calling "EndInvoke" with "1" argument(s): "You cannot call a method on a null-valued expression."

If you see this error message, check your code for a Write-Output, Write-Host, Write-Error, which are being passed a $null argument.

For example:

$something = $null # Unexpectedly
Write-Output $something

While this has no effect outside of PoshRSJob, in this case it will trigger the above error. A fuller exception is as below:

ErrorRecord                 : Exception calling "EndInvoke" with "1" argument(s): "You cannot call a method on a null-valued expression."
WasThrownFromThrowStatement : False
Message                     : Exception calling "EndInvoke" with "1" argument(s): "You cannot call a method on a null-valued expression."
Data                        : {}
InnerException              : System.Management.Automation.CmdletInvocationException: You cannot call a method on a null-valued expression. ---> 
                              System.Management.Automation.RuntimeException: You cannot call a method on a null-valued expression.
                                 at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
                                 at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
                                 at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
                                 at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
                                 at System.Management.Automation.Interpreter.Interpreter.Run(InterpretedFrame frame)
                                 at System.Management.Automation.Interpreter.LightLambda.RunVoid1[T0](T0 arg0)
                                 at System.Management.Automation.PSScriptCmdlet.RunClause(Action`1 clause, Object dollarUnderbar, Object inputToProcess)
                                 at System.Management.Automation.PSScriptCmdlet.DoProcessRecord()
                                 at System.Management.Automation.CommandProcessor.ProcessRecord()
                                 --- End of inner exception stack trace ---
                                 at System.Management.Automation.Runspaces.AsyncResult.EndInvoke()
                                 at System.Management.Automation.PowerShell.EndInvoke(IAsyncResult asyncResult)
                                 at CallSite.Target(Closure , CallSite , Object , Object )
TargetSite                  : Void ConvertToMethodInvocationException(System.Exception, System.Type, System.String, Int32, System.Reflection.MemberInfo)
StackTrace                  :    at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
                                 at lambda_method(Closure , Object[] , StrongBox`1[] , InterpretedFrame )
HelpLink                    : 
Source                      : System.Management.Automation
HResult                     : -2146233087

$PSCmdlet.ShouldProcess() does not return any value

Functions which have SupportsShouldProcess will work as normal, however, the What If: output which would normally be output to screen by $PSCmdlet.ShouldProcess() outputs nothing with an RSJob. This is because it doesn't write to any normal streams that are accessible within jobs.