Cannot bind argument to parameter 'InputObject' because it is null

Question

I have a powershell script that measures download time on some pages, however I get the error above, I am unsure what I am doing wrong

error is

Cannot bind argument to parameter 'InputObject' because it is null.

function ResponseTime($CommonName,$URL, $environment) 
{ 
    $Times = 5
    $i = 0 
    $TotalResponseTime = 0 
      Write-HOst $URL
    While ($i -lt $Times) { 
        $Request = New-Object System.Net.WebClient 
        $Request.UseDefaultCredentials = $true 
        $Start = Get-Date 
        Write-HOst $URL
        $PageRequest = $Request.DownloadString($URL) 
        $TimeTaken = ((Get-Date) - $Start).TotalMilliseconds 
        $Request.Dispose() 
        $i ++ 
        $TotalResponseTime += $TimeTaken 
    } 

    $AverageResponseTime = $TotalResponseTime / $i 
    Write-Host Request to $CommonName took $AverageResponseTime ms in average -ForegroundColor Green 

    $details = @{            
        Date             = get-date              
        AverageResponseTime     = $AverageResponseTime              
        ResponseTime      = $Destination 
        Environment = $environment
    }                           
    $results += New-Object PSObject -Property $details
    $random = Get-Random -minimum 1 -maximum 30
    Start-Sleep -s $random
} 

#PRODUCTION
ResponseTime -commonname 'app homepage' -URL 'https://url1' -environment 'PRODUCTION'
ResponseTime -commonname 'department homepage' -URL 'https://url2' -environment 'PRODUCTION'

$results | export-csv -Path c:\so.csv -NoTypeInformation

On which line do you get the error message? What did you try to debug your code? — Clijsters, Oct 06 '17 at 11:53
Do you have quotes around the message after `Write-Host`? i.e. `Write-Host "Request to $CommonName took $AverageResponseTime ms in average" -ForegroundColor Green ` — JohnLBevan, Oct 06 '17 at 11:55
in the last line that I just added to the original question, I missed that sorry. — Luis Valencia, Oct 06 '17 at 11:55
ps. FYI it's generally recommended that you avoid `Write-Host` for most scenarios; see this post for more: https://stackoverflow.com/questions/38523369/write-host-vs-write-information-in-powershell-5 — JohnLBevan, Oct 06 '17 at 11:56
Yeah, so `$results` is empty. It should be a list-like object where you add your items to. — Clijsters, Oct 06 '17 at 11:57
NB: Results is defined within your function; but you're referencing it outside of your function; i.e. you're looking at a different (undefined/null) variable. — JohnLBevan, Oct 06 '17 at 12:01
The (write) scope of the `$results` variable is within your function. You will need to give `$results` a global scope: `$global:results` (note also that when you use the addition assignment operator (`+=`) the first instance will be `$Null`) or better return the `$results` from your function and assign it to a global `$results`: `$Results = ResponseTime -commonname 'app homepage' ... `$Results += ResponseTime -commonname 'department homepage'...` — iRon, Oct 06 '17 at 12:05
Is the last line - which was added with your edit really the last line of your code or just placed there for instructional purposes? — Clijsters, Oct 06 '17 at 12:07

Clijsters · Answer 1 · 2017-10-06T12:06:33.550

Reviewing your last edit, it seems that $results simply returns $null (As your error says)

The only line setting $results is $results += New-Object PSObject -Property $details

It is not in the scope of your Export-CSV call and - even if it would, $results could be empty, if this line is not called.

You should IMHO set it to e.g. an ArrayList like follows:

$results = New-Object -TypeName System.Collections.ArrayList

And add items to it via

$times = ResponseTime -commonname '' #etc
$results.Add($times) | Out-Null

This gives you an ArrayList - even if there are no items in it - which can easily be transformed to CSV and other formats.

JohnLBevan · Accepted Answer · 2017-10-06T13:43:44.343

@Clijsters has given the correct answer; i.e. the issue being the scope of your $results variable.

This answer just provides a bit of a code review to help you with other bits going forwards...

function Get-ResponseTime { 
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [string]$CommonName
        ,
        [Parameter(Mandatory = $true)]
        [string]$URL
        , 
        [Parameter(Mandatory = $true)]
        [string]$Environment
        , 
        [Parameter(Mandatory = $false)]
        [int]$Times = 5
    )    
    [System.Int64]$TotalResponseTime = 0 
    [System.Diagnostics.Stopwatch]$stopwatch = New-Object 'System.Diagnostics.Stopwatch'
    Write-Verbose "Processing URL: $URL"
    1..$times | foreach-object {
        [System.Net.WebClient]$Request = New-Object 'System.Net.WebClient' 
        $Request.UseDefaultCredentials = $true 
        Write-Verboset "Call $_ to URL: $URL"
        $stopwatch.Restart()
        $PageRequest = $Request.DownloadString($URL) 
        $stopwatch.Stop()
        $TimeTaken = $stopwatch.Elapsed.TotalMilliseconds 
        $Request.Dispose() 
        $TotalResponseTime += $TimeTaken 
    } 

    $AverageResponseTime = $TotalResponseTime / $Times 
    Write-Verbose "Request to $CommonName took $AverageResponseTime ms on average" 

    $details = @{            
        Date             = get-date              
        AverageResponseTime     = $AverageResponseTime              
        #ResponseTime      = $Destination #this is not declared anywhere / don't know what this field's for
        Environment = $environment
    }                           
    Write-Output (New-Object 'PSObject' -Property $details)
    #do you really want a delay here?  Doesn't make much sense... may make sense to include a delay in the above loop; i.e. to stagger your tests?
    #$random = Get-Random -minimum 1 -maximum 30
    #Start-Sleep -s $random
} 

#PRODUCTION
[PSObject[]]$results = @(
    (Get-ResponseTime -commonname 'app homepage' -URL 'https://url1' -environment 'PRODUCTION' -Verbose)
    ,(Get-ResponseTime -commonname 'department homepage' -URL 'https://url2' -environment 'PRODUCTION' -Verbose)
)
$results | Export-Csv -LiteralPath 'c:\so.csv' -NoTypeInformation

Use verb-noun function names (e.g. Get-Item). What is the naming convention for Powershell functions with regard to upper/lower case usage?
Use "Cmdlets" (Advanced Functions) instead of (Basic) Functions; they're basically the same thing, only tagged with [Cmdletbinding()]. The reason for this you get support for functionality such as verbose output. http://www.lazywinadmin.com/2015/03/standard-and-advanced-powershell.html
Use a stopwatch to time processes (you could also use measure-command; but any output would be suppressed / consumed by the measure-command function). Timing a command's execution in PowerShell
Have your cmdlet output its values to the pipeline via Write-Output (or you can leave off the function name; any output caused by placing a variable with nothing to process it will be fed to the pipeline; i.e. write-object $a is the same as a line solely consisting of $a).
Capture the output into your $results variable outside of the function, and handle the results there.

Cannot bind argument to parameter 'InputObject' because it is null

2 Answers2