[IS2Telephony phoneSignalBars] causes error on phone with no SIM card

[GaitherStephens]

Code:

    try{
      storage.phoneSignalBars = [IS2Telephony phoneSignalBars];
    }catch(err) {
      alert(err);
    }

Resulting error message: 'this call must be made on the main thread'

Device: iPhone 6 jailbroken on 9.3.3