Invalid Key Type (Somehow)

InvalidKeyTypeExample.ps1

$AllProperties = @(
    'Title',
    'Subject',
    'Author',
    'Keywords',
    'Comments',
    'Template',
    'Last Author',
    'Revision Number',
    'Application Name',
    'Last Print Date',
    'Creation Date',
    'Last Save Time',
    'Total Editing Time',
    'Number of Pages',
    'Number of Words',
    'Number of Characters',
    'Security',
    'Category',
    'Format',
    'Manager',
    'Company',
    'Number of Bytes',
    'Number of Lines',
    'Number of Paragraphs',
    'Number of Slides',
    'Number of Notes',
    'Number of Hidden Slides',
    'Number of Multimedia Clips'
)

[System.Collections.ArrayList]$NewColumns = @()

$AllProperties | %{
    [void]$NewColumns.Add(@{
        'Name' = $_;
        'Expression' = {1}
    })
}

$true | select $NewColumns
# This returns the following error:
# The "Name" key has a type, System.Management.Automation.PSObject, that is not valid; expected type is System.String