Why the argument is empty or null - windows

Question

everyone
I'm a novice at Powershell.
My script gather Windows Event Viewer logs and export data to csv files. If the input is empty then is used the default values.
But it crashes:
"Export-Csv: Unable to validate argument for "Path" parameter. The argument is empty or NULL. Specify a non-empty, non-null argument and then run the command again."
Could explain to me why??
function exportLogs
{
[CmdletBinding()]
param (
$exportFolder=(Read-Host -prompt "exportFolder"),
$applicatiomLogs=(Read-Host -prompt "applicationLogs"),
$systemLogs=(Read-Host -prompt "systemLogs"),
$fromDate=(Read-Host -prompt "fromDate"),
$eventTypes=(Read-Host -prompt "eventTypes")
)
$comp = $env:computername
$now=Get-Date
#check empty input and assign default values
if (!$exportFolder) { [String]$exportFolder="D:\temp\" }
if (!$applicationLogs) {
$applicationLogs="True"
[System.Convert]::ToBoolean($applicationLogs)
}
if (!$systemLogs) {
$systemLogs="True"
[System.Convert]::ToBoolean($systemLogs)
}
if (!$fromDate) { [DateTime]$fromDate=$now.AddDays(-30) }
if (!$eventtypes) { [String[]]$eventtypes=("Error", "Warning") }
if ($applicationLogs)
{
$exportFile = $exportFolder + "applicationLogs_" + $now.ToString("yyyyMMddHHmmss") + ".csv"
$exportedLog = get-eventlog -ComputerName $comp -log "Application" -After $fromDate -EntryType $eventTypes
exportCsv($exportedLog, $exportFile)
}
if ($systemLogs)
{
$exportFile = $exportFolder + "systemLogs_" + $now.ToString("yyyyMMddHHmmss") + ".csv"
$exportedLog = get-eventlog -ComputerName $comp -log "System" -After $fromDate -EntryType $eventTypes
exportCsv($exportedLog, $exportFile)
}
}
function exportCsv([String]$exportedLog, [String]$exportFile)
{
$el_sorted = $exportedLog | Sort-Object TimeGenerated
Write-Host Exporting to $exportFile
$el_sorted|Select MachineName, TimeGenerated, EntryType, Source, Message | Export-CSV $exportFile -NoTypeInfo
}

Answer 1

Try this refactor... (run on the default Windows Sandbox on Win10)
function New-LogExport
{
Param
(
[String]$exportedLog,
[String]$exportFile
)
$el_sorted = $exportedLog |
Sort-Object TimeGenerated
Write-Host "Exporting to $exportFile"
$el_sorted |
Select-Object MachineName,
TimeGenerated,
EntryType,
Source,
Message |
Export-Csv -Path $exportFile -NoTypeInfo
}
function Start-ExportLogs
{
[CmdletBinding()]
param
(
$exportFolder = (Read-Host -prompt 'exportFolder'),
$applicatiomLogs = (Read-Host -prompt 'applicationLogs'),
$systemLogs = (Read-Host -prompt 'systemLogs'),
$fromDate = (Read-Host -prompt 'fromDate'),
$eventTypes = (Read-Host -prompt 'eventTypes')
)
$comp = $env:computername
$now = Get-Date
if (!$exportFolder)
{[String]$exportFolder = 'C:\temp'}
if (!$applicationLogs)
{
$applicationLogs = 'True'
[System.Convert]::ToBoolean($applicationLogs)
}
if (!$systemLogs)
{
$systemLogs = 'True'
[System.Convert]::ToBoolean($systemLogs)
}
if (!$fromDate)
{[DateTime]$fromDate = $now.AddDays(-30)}
if (!$eventtypes)
{[String[]]$eventtypes = ('Error', 'Warning')}
if ($applicationLogs)
{
$exportFile = "$exportFolder\applicationLogs_$($now.ToString('yyyyMMddHHmmss')).csv"
$getEventLogSplat = #{
ComputerName = $comp
LogName = 'Application'
EntryType = $eventTypes
After = $fromDate
}
$exportedLog = Get-EventLog #getEventLogSplat
New-LogExport -exportedLog $exportedLog, -exportFile $exportFile
}
if ($systemLogs)
{
$exportFile = "$exportFolder\systemLogs_$($now.ToString('yyyyMMddHHmmss')).csv"
$getEventLogSplat = #{
ComputerName = $comp
LogName = 'System'
EntryType = $eventTypes
After = $fromDate
}
$exportedLog = Get-EventLog #getEventLogSplat
}
New-LogExport -exportedLog $exportedLog -exportFile $exportFile
}
# Results
<#
exportFolder:
applicationLogs:
systemLogs:
fromDate:
eventTypes:
True
True
Exporting to C:\temp\applicationLogs_20210120143659.csv
Exporting to C:\temp\systemLogs_20210120143659.csv
#>