Public/Get-TrelloCustomFieldOption.ps1

function Get-TrelloCustomFieldOption {
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory, ValueFromPipeline)]
        [ValidateNotNullOrEmpty()]
        [pscustomobject]$CustomField
    )
    begin {
        $ErrorActionPreference = 'Stop'
    }
    process {
        try {
            if ('options' -notin $CustomField.PSObject.Properties.Name) {
                throw 'Custom field does not support options.'
            } else {
                $uri = '{0}/customField/{1}/options?{2}' -f $script:baseUrl, $CustomField.Id, $trelloConfig.String
                Invoke-RestMethod -Uri $uri
            }
        } catch {
            Write-Error $_.Exception.Message
        }
    }
}