Null check operator used on a null value

[GPSxtreme]

Description

package version: ^2.3.9

Got this crash log recorded on crashlytics,

 Fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: Null check operator used on a null value
       at Navigator.of(navigator.dart:2830)
       at DropdownButton2State._getRect(dropdown_button2.dart:1357)
       at DropdownButton2State.didChangeMetrics(dropdown_button2.dart:1344)
       at WidgetsBinding.handleMetricsChanged(binding.dart:755)
        

full trace: trace.txt