How to validate empty field in azure task in build pipeline using powershell - azure-pipelines-release-pipeline

Question

I'm creating new VSTS/TFS extension in azure build pipeline.
In that extension one field accepts a file path and it is optional field.
In powershell script, i want to validate the field, if no input is provided then i have to ignore, otherwise i have to check whether input is path of .config file or not.
$ConfigFileName = Get-VstsInput -Name 'ConfigFilePath'
if (!(Test-Path $ConfigFileName))
{
Write-Host "Configuration file doesn't exist."
"##vso[task.complete result=Failed]"
throw "Configuration file doesn't exist."
}
if([IO.Path]::GetExtension($ConfigFileName) -ne '.config')
{
Write-Host "Invalid configuration file.File type must be of .config"
"##vso[task.complete result=Failed]"
throw "Invalid configuration file.File type must be of .config"
}
I have validated like above, but when user not provided any input then also the $ConfigFileName variable filled with mapping path that is $ value.
How to check if input provided to that field is empty or not?

Answer 1

For filePath type input field, the default value is source directory (Build.SourcesDirectory, e.g. D:\a\1\s). So, you could check whether the value is not equal to the source directory.
For example:
{
"name": "filePathSelect",
"type": "filePath",
"label": "test select Path",
"required": false,
"defaultValue": "",
"helpMarkDown": "test select path"
}
PowerShell:
Write-Host "get select file path value"
$fileSelectPathValue = Get-VstsInput -Name filePathSelect
Write-Host "select file path value is $fileSelectPathValue"
Write-Host "default path $env:Build_SourcesDirectory"
if([string]::IsNullOrEmpty($fileSelectPathValue)){
Write-Host "Selected File path is empty"
}
elseif(($fileSelectPathValue -eq $env:Build_SourcesDirectory) -or !(Test-Path $fileSelectPathValue))
{
Write-Host "select path is invalid"
}
else
{
Write-Host "select path is valid"
}
If the input type is string, then you just need to check whether the value is null or empty [string]::IsNullOrEmpty.