Common/Model/Notify.php
public function addInvoice(InvoiceInterface $invoice)
    {
        if (!$this->invoices->contains($invoice)) {
            $this->invoices->add($invoice);
        }

        return $this;
    }
public function addInvoice(InvoiceInterface $invoice)
    {
        if (!$this->invoices->contains($invoice)) {
            $this->invoices->add($invoice);
        }

        return $this;
    }
Adds the invoice.

@param InvoiceInterface $invoice

@return Notify