How to check that an argument to be not null when other argument is not present

Below is the C# code where I am creating this powershell cmdlt which has two argument MaxAge and ContinuationToken. I would like

  • MaxAge to be mandatory when Continuation token is not provided.
  • ContinuationToken if provided to be mandatory and MaxAge to be optional.
  • ContinuationToken cannot be null whenever it is provided and it should be prompted to user to provide that value
I am able to achieve my 1st two scenario but unable to achieve the last one. Below is my pwshell cmdlet and my C# code. Please advice:

[Cmdlet(VerbsCommon.Get, "ChangedRecordings", DefaultParameterSetName = GetChangedRecordingsCmd.ParamSetCloud)]
public class GetChangedRecordingsCmd : PwshCmd

protected const string ParamSetCloud = "Cloud";
protected const string ParamSetFile = "File";

[Parameter(Mandatory = true,
Position = 0, ParameterSetName = ParamSetCloud,
ValueFromPipeline = true,
ValueFromPipelineByPropertyName = true, HelpMessage = "Provide the maximum age of recordings from the change feed")]
[Parameter(Mandatory = false, ParameterSetName = ParamSetFile)]
public TimeSpan MaxAge { get; set; }

[Parameter(Position = 1,Mandatory = true,
ValueFromPipeline = true, ParameterSetName = ParamSetFile,
ValueFromPipelineByPropertyName = true, HelpMessage = "Provide a continuation token for the change feed")]

public string ContinuationToken { get; set; }

protected override void BeginProcessing()
if (ParameterSetName.Equals(ParamSetFile) && string.IsNullOrWhiteSpace(ContinuationToken))
WriteWarning("Continuation Token can't be null. Please pass a valid Continuation Token");

protected override void ProcessRecord()
//My opeartions
WriteObject(new { ContinuationToken = result, Recordings = recs });

Powershell Cmndlet(Token File path contains the Continuation token. As per above scenario that can be blank and I need to handle this in C#)

param (
$TokenFilePath = 'C:\Users\Desktop\ContinuationToken.txt',
$MaxAge = '2'
$existingToken = Get-Content -Path $TokenFilePath
$recordings = Get-ChangedRecordings -ContinuationToken $existingToken -MaxResults 10
Write-Host $recordings.Recordings.Count
$recordings.ContinuationToken|Set-Content -Path $TokenFilePath
$recs = $recordings.Recordings