Convert common values to Powershell boolean values $true and $false

ConvertTo-Boolean.ps1

function ConvertTo-Boolean
{
  param
  (
    [Parameter(Mandatory=$false)][string] $value
  )
  switch ($value)
  {
    "y" { return $true; }
    "yes" { return $true; }
    "true" { return $true; }
    "t" { return $true; }
    1 { return $true; }
    "n" { return $false; }
    "no" { return $false; }
    "false" { return $false; }
    "f" { return $false; } 
    0 { return $false; }
  }
}

What if it's none of those values? Then it just returns $null? How about deciding on whitelisting or blacklisting, and also condensing the code a drop, such as:

function ConvertTo-Boolean
{
  param
  (
    [Parameter(Mandatory=$false,ValueFromPipeline=$true)][string] $value
  ) 
  return @("y", "t", "true", "1").Contains($value)
}

You can also just use the [bool]::Parse or [bool]::TryParse functions, but then you won't have all the fancy scenarios which you enumerated.