Actual Behaviour
The app crashes if the app was connected to the PSLab via WiFi, PSLab is turned off and app is closed.

Expected Behaviour
The app should never crash.

Steps to reproduce it
0. Power on PSLab with ESP01

1. Connect app to PSLab via WiFi
2. Power off PSLab
3. Wait until phone notices that WiFi is offline and app shows disconnect message
4. Close app

---> Crash

FATAL EXCEPTION: main
Process: io.pslab, PID: 16813
java.lang.RuntimeException: Unable to destroy activity {io.pslab/io.pslab.activity.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void io.pslab.communication.CommunicationHandler.close()' on a null object reference
at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4244)
at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:4262)
at android.app.ActivityThread.-wrap6(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1551)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6165)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void io.pslab.communication.CommunicationHandler.close()' on a null object reference
at io.pslab.communication.ScienceLab.disconnect(ScienceLab.java:2910)
at io.pslab.activity.MainActivity.onDestroy(MainActivity.java:520)
at android.app.Activity.performDestroy(Activity.java:6889)
at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1175)
at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4231)
at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:4262) 
at android.app.ActivityThread.-wrap6(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1551) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6165) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)

Screenshots of the issue
Video: https://github.com/user-attachments/assets/99412b60-40d6-461a-a9aa-4dc043c279ab

Would you like to work on the issue?
Yes, I will open a PR in a short time.