help.ps1

[cmdletbinding(SupportsShouldProcess=$true,DefaultParameterSetName="User")]
Param(
    [Parameter(Mandatory=$true,
               Position=0,
               ParameterSetName="User",
               ValueFromPipeline=$true,
               ValueFromPipelineByPropertyName=$true)]
    [Microsoft.ActiveDirectory.Management.ADUser[]]
    [Parameter(Mandatory=$true,
               Position=0,
               ParameterSetName="GroupMember",
               ValueFromPipeline=$true,
               ValueFromPipelineByPropertyName=$true)]
    [Microsoft.ActiveDirectory.Management.ADPrincipal[]]
    $Identity,
)

$gm = get-adgroupmember...

New-CADirectory : Cannot bind argument to parameter 'Identity' because it is an empty array.
At line:1 char:7
+ $gm | New-CADirectory -SubjectName test -intake 2016 -WhatIf
+       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (CN=username,OU=2...org,DC=INTERNAL:PSObject) [New-CADirectory], ParameterB
   indingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyArrayNotAllowed,New-CADirectory
    
$u = get-adgroupmember | get-aduser
$u | New-CADirectory -SubjectName test -intake 2016 -WhatIf

What if: Performing the operation "Create Directory" on target "\path\test\username".
etc...