Get-ADSIComputer $ComputerName

[lazywinadmin]

When using Get-ADSIComputer $ComputerName

I'm getting the following error

Get-AdsiComputer $env:COMPUTERNAME
Get-ADSIComputer : A positional parameter cannot be found that accepts argument ''.
At line:1 char:1

• Get-AdsiComputer $env:COMPUTERNAME

•   + CategoryInfo          : InvalidArgument: (:) [Get-ADSIComputer], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Get-ADSIComputer
  

[Get-Ryan]

The error is due to not listing a position for any of the parameters in the function. You mention in your guidelines to use explicit parameter names and not assume position, which is good, but if you don't have position set for any of the parameters, you prevent the use of your function without explicitly naming the parameters when calling it.

So you either need to always use named parameters:
Get-ADSIComputer -Identity $env:COMPUTERNAME

Or adjust the $Identity parameter line to allow it to accept positional input:
param ([Parameter(Mandatory=$true,Position=0,ParameterSetName="Identity")])