code: public InvoiceCollection postAccountInvoice(final String accountCode, final Invoice invoice) {
          return doPOST(Accounts.ACCOUNTS_RESOURCE + "/" + accountCode + Invoices.INVOICES_RESOURCE, invoice, InvoiceCollection.class);
      }
docs: Post an invoice: invoice pending charges on an account
  <p>
  Returns an invoice collection
  
  @param accountCode
  @return the invoice collection that was generated on success, null otherwise