Operator join cannot accept the argument [*nothing*]

Hi, For my application I am trying to read all the received SMS and store them in Firebase. but some SMS doesn’t have a phone number (for ex: SMS from Telecom companies) due to this, the app crashes as it is expecting a phone number, but doesn’t get one. I tried to eliminate it by checking if the string was empty. but the problem still exists.

Try this:

If(PhoneNumber == “”)
Store to firebase “Something”
Store to Firebase PhoneNumber

are you aware, that your solution will work only while your app is up and running?