Creating files in Document library in SharePoint 2010 using Powershell

I am using below script to copy files from one library to another:

$SourceWebURL = "http://sitecollection/sites/site" 
$SourceLibraryTitle = "doclib" 
$DestinationWebURL = "http://sitecollection/sites/site" 
$DestinationLibraryTitle = "doclib" 
$ssite = Get-SPSite $SourceWebURL
$sweb = $ssite.OpenWeb("subsite")
$dsite = Get-SPSite $DestinationWebURL 
$dweb = $dsite.OpenWeb("Archivesubsite")
$sList = $sWeb.Lists | ? {$_.Title -eq $SourceLibraryTitle} 
$dList = $dWeb.Lists | ? {$_.title -like $DestinationLibraryTitle} 
$AllFolders = $sList.Folders 
$RootFolder = $sList.RootFolder 
$RootItems = $RootFolder.files 

foreach($Folder in $AllFolders)
{
echo $Folder.url
    foreach($Item in $Folder)
    {
        $sBytes = $RootItem.OpenBinary() 
            $dFile  = $dList.RootFolder.Files.Add($Item.Name, $sBytes, $true) 
        $dFile.Update() 
    }
}

I want to loop in each folder in doclib and create the files in folders in destination library. Error I am getting is : You cannot called a method on null valued expression.