/**
  * This method calculates the payment amount for the customers.
  *
  * @param cgDocs
  * @param begin
  * @param end
  * @return
  */
 private KualiDecimal calculatePaymentAmountForCustomer(
     Collection<ContractsGrantsInvoiceDocument> cgDocs, java.sql.Date begin, java.sql.Date end) {
   KualiDecimal invoiceAmt = KualiDecimal.ZERO;
   if (ObjectUtils.isNotNull(cgDocs) && !cgDocs.isEmpty()) {
     for (ContractsGrantsInvoiceDocument cgDoc : cgDocs) {
       if (ObjectUtils.isNotNull(cgDoc.getBillingDate())) {
         if (ObjectUtils.isNotNull(begin)) {
           if (cgDoc.getBillingDate().compareTo(begin) >= 0
               && cgDoc.getBillingDate().compareTo(end) <= 0) {
             invoiceAmt = invoiceAmt.add(cgDoc.getPaymentAmount());
           }
         } else {
           if (cgDoc.getBillingDate().compareTo(end) <= 0) {
             invoiceAmt = invoiceAmt.add(cgDoc.getPaymentAmount());
           }
         }
       }
     }
   }
   return invoiceAmt;
 }