Function pipeline support, can't bind argument to parameter - powershell

Question

I created following simple funcion, where the parameter supports input from pipeline:
function Write-Log {
[CmdletBinding()]
param (
# Lines to log
[Parameter(Mandatory , ValueFromPipeline )]
[string[]]
$PipeLineLoglines
)
process {
Write-Host $_
}
}
If I call the function via e.g. :
"test1", "test2" | Write-Log
It works as expected, but if I'm forwarding an empty string down the pipeline I get the folowing error:
C:\> "test1", "", "test2" | Write-Log
test1
Write-Log : Cannot bind argument to parameter 'PipeLineLoglines' because it is an empty string.
At line:1 char:24
+ "test1", "", "test2" | Write-Log
+ ~~~~~~~~~
+ CategoryInfo : InvalidData: (:String) [Write-Log], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyStringNotAllowed,Write-Log
test2
I'm using PowerShell.Core:
C:\> $PSVersionTable
Name Value
---- -----
PSVersion 6.2.0
PSEdition Core
GitCommitId 6.2.0
OS Microsoft Windows 10.0.17763
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
Can someone explain why an empty string causes this error?
Thx

Answer 1

It's because the parameter is Mandatory, and it's considered that an empty string did not satisfy that condition. Given that there are specific validation attributes to test for that, I don't like this behavior, but that's the way it is.
There is an attribute that can help you though, [AllowEmptyString()]:
function Write-Log {
[CmdletBinding()]
param (
# Lines to log
[Parameter(Mandatory , ValueFromPipeline )]
[AllowEmptyString()]
[string[]]
$PipeLineLoglines
)
process {
Write-Host $_
}
}