getLocation Null after turn-off - turn-on device location

Hi Everyone,
Firstly, Thank you for share the source code. It is very useful with me.
But there are an issue persist.
procedure:
1. Turn on device location 
2. Run app
3. Turn off device location 
4. Pick location on the app => showToast("Couldn't get the location. Make sure location is enabled on the device");

Please help me how can fix this issue?
Thank you for your help.