Send SMS null to null

what you want to ask is what is the reason for sending a short message showing null? The reason why sending SMS shows null is that the number of the SMS receiver is wrong, the SMS receiver's mobile phone is out of service, and the SMS receiver's mobile phone is full.

1. The number of the short message receiver is wrong or does not exist, which leads to the sending failure and returns null.

2. The short message receiver's mobile phone is out of service, or the signal is not good, which leads to the failure of sending the short message and returns null.

3. The mobile phone of the short message receiver is full, which leads to the inability to receive new short messages, and also leads to the failure of sending short messages and returns null.