When a private number makes a call to an SMSLib driven modem, SMSLib
crashes. The last debug lines before the crash are similar to the following:

12719  22:59:38 [main] DEBUG org.smslib.ModemDriver  - SEND :AT+CPMS="SM"(cr)
12719  22:59:38 [main] DEBUG org.smslib.ModemDriver  - RECV :OK(cr)
12719  22:59:38 [main] DEBUG org.smslib.ModemDriver  - SEND :AT+CMGL=4(cr)
12750  22:59:38 [main] DEBUG org.smslib.ModemDriver  - RECV :+CPMS:
0,35,0,35,0,185(cr)OK(cr)
12766  22:59:38 [main] ERROR org.smslib.ModemGateway  - *****
12766  22:59:38 [main] ERROR org.smslib.ModemGateway  - Unhandled SMS in
inbox, skipping!
12766  22:59:38 [main] ERROR org.smslib.ModemGateway  - Err: For input
string: "OK"
12766  22:59:38 [main] ERROR org.smslib.ModemGateway  - *****
java.lang.NullPointerException
        at org.smslib.ModemGateway.readMessagesPDU(ModemGateway.java:458)
        at org.smslib.ModemGateway.readMessages(ModemGateway.java:107)
        at org.smslib.Service.readMessages(Service.java:268)
        at org.smslib.Service.readMessages(Service.java:208)
        at org.smslib.smssvr.SMSSvr.readMessages(SMSSvr.java:252)
        at org.smslib.smssvr.SMSSvr.execute(SMSSvr.java:297)
        at org.smslib.smssvr.SMSSvr.main(SMSSvr.java:390)

This error happens only for private-number callers (where CLIP ids are
missing).