getNumberSMS() is not working

[tgisop]

Hi,
I am trying to get the SMS number of Sim800l but the function is not working.
All the other function are OK
the code is simple ::::

String SMSBody, SMSNum
.
.
void loop()
.
byte index = GSM.checkForSMS();
SMSBody=GSM.readSms(index);
SMSNum=GSM.getNumberSms(index);

Serial.println((String)"SMSBody :"+SMSBody);
Serial.println((String)"SMSNum :"+SMSNum);

and the results are
SMSBody :Turnon
SMSNum :

Can you help me?
Can you please edit the README.md comments?

[vittorioexp]

Please try to execute the example [readSms.ino](https://github.com/vittorioexp/Sim800L-Arduino-Library-revised/blob/master/examples/readSms/readSms.ino)
What's the output of this?