Current user as default for PSCredential parameter of custom CmdletBinding - powershell

Question

Here's a repro of my Powershell scenario:
function Call-Api {
[CmdletBinding()]
param(
[Parameter(Position = 0, Mandatory = $false)]
[System.Management.Automation.Credential()]
[System.Management.Automation.PSCredential]
$Credential = [System.Management.Automation.PSCredential]::Empty
)
Invoke-RestMethod -Uri "http://localhost/api" -Method Get -Credential $Credential
}
The API has Basic Auth. If I call it like this:
$pwd = ConvertTo-SecureString "secret!" -AsPlainText -Force
$cred = New-Object System.Management.Automation.PSCredential ("username", $pwd)
Call-Api $cred
Then I get a proper response. But if I call it without credentials like this:
Call-Api
I get:
Invoke-RestMethod : Object reference not set to an instance of an object.
I could of course do an if...else thing switching on whether $Credential is set or not, but that's not very elegant. From the relevant docs I understand that the default value of that cmdlet is "the current user".
How can I do something similar? What default do I set for $Credential so that it is the current user?

Answer 1

You can remove the Empty Credential that you are defining as default (I believe this is overwriting the cmdlets own default of current user), then use splatting and only add the $Credential Parameter if it present. If it's not present it will use the cmdlets own default value.
function Call-Api {
[CmdletBinding()]
param(
[Parameter(Position = 0)]
[System.Management.Automation.Credential()]
[System.Management.Automation.PSCredential]
$Credential
)
$params = #{}
$params['Uri'] = "http://google.com"
$params['Method'] = "Get"
if ($Credential) { $params['Credential'] = $Credential }
Invoke-RestMethod #params
}