/** Returns the memo included by the merchant in the payment request, or null if not found. */
 @Nullable
 public String getMemo() {
   if (paymentDetails.hasMemo()) return paymentDetails.getMemo();
   else return null;
 }
 /** Returns the memo included by the merchant in the payment request. */
 public String getMemo() {
   return paymentDetails.getMemo();
 }