Report Saved Search to excel, with custom attributes

I would like to write a report to excel based on a saved search. I also need to write a custom attribute 'Revision No' to excel.

In the if block the custom attribute is written to the terminal but it doesn't write to Excel. 

$SavedSearch = 'PW test'
$timestamp = Get-Date -Format "yyyyMMdd_HHmmss"
$path = "C:\Users\user\Documents\00_Dev\powershell\pw\logs\weekly_report_$timestamp.xlsx"

# Define the column headers you want to include in the Excel file
$desiredColumnHeaders = @("Name", "Revision")

$docs = Get-PWDocumentsBySearch -searchName $SavedSearch
$docs = $docs | Select-Object -Property Name, @{Name="Revision";Expression={$_.CustomAttributes.Revision_Nos}}

# Check if any documents are returned
if ($docs.Count -gt 0) {
    # Get the property names of the first document and display them
    $propertyNames = $docs[0] | Get-Member -MemberType Properties | Select-Object -Property Name, @{Name="Revision";Expression={$_.CustomAttributes.Revision_Nos}}
    Write-Output "Available properties:"
} else {
    Write-Output "No documents found in the saved search."

# Filter the properties you want to keep for each document
$filteredDocuments = $docs | Select-Object -Property $desiredColumnHeaders, @{Name="Revision";Expression={$_.CustomAttributes.Revision_Nos}}

# Export the filtered documents to an Excel file
$filteredDocuments | Export-Excel -Path $path -WorksheetName "Documents" -AutoSize

Any help is appreciated