Powershell CheckIn Throwing null-valued expression error

Question

I've got a script that goes through subwebs of a sie and adds a webpart to the page. Everything is functioning correctly, until it's time to check the file in. I get the following error:

You cannot call a method on a null-valued expression. At D:\scripts\AddWebPart.ps1:73 char:54 + $publishingPage.ListItem.File.CheckIn <<<< ($comment) + CategoryInfo : InvalidOperation: (CheckIn:String) [], RuntimeException + FullyQualifiedErrorId : InvokeMethodOnNull

This is the line that blows up:

$publishingPage.ListItem.File.CheckIn("Added Content Editor Webpart")

Also tried the other overload:

$publishingPage.ListItem.File.CheckIn("Added Content Editor Webpart", [Microsoft.SharePoint.SPCheckinType]::MajorCheckIn)

With the same result. What am I missing? Everything seems legit to me.

---

Adding more code as requested. This is the working version*. [It works on my dev environment, but blows up on the staging environment due to something unrelated to my original question.

#Add SharePoint assemblies
[system.reflection.assembly]::loadwithpartialname("microsoft.sharepoint")
[system.reflection.assembly]::loadwithpartialname("microsoft.sharepoint.publishing")

function add-ContentEditorWebPart($siteUrl, $webUrl)
{
    #Set up default variables
    $siteUrl = $siteUrl.ToString()
    $webUrl = $webUrl.ToString()
    #$content is going to be the contents of the content editor webpart [google remarketing tag in this case]
    $content = '<!--script here-->'
    $webpartzone = "bottomWebPart"
    $index = 0
    $comment = "Google Remarketing Script Added"

    #Get site and web objects
    $site = new-Object Microsoft.SharePoint.SPSite($siteUrl)
    $web = $site.OpenWeb($webUrl)
    foreach ($subweb in $web.Webs)
    {
        if ([Microsoft.SharePoint.Publishing.PublishingWeb]::IsPublishingWeb($subweb)) {
            write-host "Reviewing pages in"$subweb.Title"site...."
            #Get the Publishing Web and pages within it
            $publishingWeb = [Microsoft.SharePoint.Publishing.PublishingWeb]::GetPublishingWeb($subweb)
            $publishingPages = $publishingWeb.GetPublishingPages()
            foreach ($publishingPage in $publishingPages)
            {
                $file = $subweb.GetFile($publishingPage.Uri.ToString())
                #Check to ensure the page isn't checked out
                if ($publishingPage.ListItem.File.CheckOutStatus -eq "None")
                {
                    Write-Host "Checking out page: " $publishingPage.Title
                    $file.CheckOut()
                    #$publishingPage.ListItem.File.CheckOut()

                    ### add webpart to page here
                    $webpartmanager = $subweb.GetLimitedWebPartManager($publishingPage.Uri, [System.Web.UI.WebControls.WebParts.PersonalizationScope]::Shared)

                    $webpart = new-object  Microsoft.SharePoint.WebPartPages.ContentEditorWebPart
                    $webpart.ChromeType = [System.Web.UI.WebControls.WebParts.PartChromeType]::None;
                    $webpart.Title = 'Google Remarketing'

                    $docXml = New-Object System.Xml.XmlDocument
                    $contentXml = $docXml.CreateElement("div");
                    $contentXml.set_InnerText($content);
                    $docXml.AppendChild($contentXml);

                    $webpart.Content = $contentXml;
                    $webpartmanager.AddWebPart($webpart, $webpartzone, $index); #the code in the brakets adds the $webpart to the mentioned zone and sets the sorting of the webpart on the first place
                    $webpartmanager.Dispose();

                    $file.Update()

                    $file.CheckIn($comment, [Microsoft.SharePoint.SPCheckinType]::MajorCheckIn)
                    $file.Approve("Approved automatically by PowerShell script.")
                    write-host "Added Content Editor Webpart and checked in file: " $publishingPage.Title "`n"

                }
                else
                {
                    #Notify user that the page is checked out and cannot be modified
                    write-host "Page"$publishingPage.Title"is currently checked out to"$publishingPage.ListItem.File.CheckedOutBy"and cannot be modified"
                }
            }
            $subweb.Dispose()
        }
        else
        {
            #Notify user that the site is not a publishing site
            write-host $subweb.Title"is not a publishing site"
        }
    }
    #Dispose of Site object
    $web.Dispose()
    $site.Dispose() 
}

As I said above, this runs great on my dev environment, but when trying to run it from the staging environment it complains about the foreach loop on line 26:

An exception was thrown when trying to enumerate the collection: " At D:\scripts\AddContenteditor.ps1:26 char:17 + foreach <<<< ($publishingPage in $publishingPages)

Answer 1

I have done a little testing and I am nearly certain that at the time you hit that line the variable $publishingPage is null.

PS C:\Users\rkaucher> $item.File.CheckOut();
You cannot call a method on a null-valued expression.
At line:1 char:20
+ $item.File.CheckOut <<<< ();
    + CategoryInfo          : InvalidOperation: (CheckOut:String) [], Runtime
   xception
    + FullyQualifiedErrorId : InvokeMethodOnNull

And I receive the error because the $item variable has gone null for some reason after I tried to refresh its instance. Please post more code! And try doing something like printing one of the properties of $publishingPage to the console.