app\models\Invoice::trashed PHP Method

    public function trashed()
    {
        if ($this->client && $this->client->trashed()) {
            return true;
        }
        return self::parentTrashed();
    }

 public function sendInvoice(Invoice $invoice, $reminder = false, $pdfString = false)
 {
     $invoice->load('invitations', 'client.language', 'account');
     $entityType = $invoice->getEntityType();
     $client = $invoice->client;
     $account = $invoice->account;
     if ($client->trashed()) {
         return trans('texts.email_errors.inactive_client');
     } elseif ($invoice->trashed()) {
         return trans('texts.email_errors.inactive_invoice');
     }
     $account->loadLocalizationSettings($client);
     $emailTemplate = $account->getEmailTemplate($reminder ?: $entityType);
     $emailSubject = $account->getEmailSubject($reminder ?: $entityType);
     $sent = false;
     if ($account->attatchPDF() && !$pdfString) {
         $pdfString = $invoice->getPDFString();
     }
     foreach ($invoice->invitations as $invitation) {
         $response = $this->sendInvitation($invitation, $invoice, $emailTemplate, $emailSubject, $pdfString);
         if ($response === true) {
             $sent = true;
         }
     }
     $account->loadLocalizationSettings();
     if ($sent === true) {
         if ($invoice->is_quote) {
             event(new QuoteWasEmailed($invoice));
         } else {
             event(new InvoiceWasEmailed($invoice));
         }
     }
     return $response;
 }