type 'Null' is not a subtype of type 'RenderBox' in type cast

[dzakybrori]

I found this error on firebase crashlytics. I think you should check this bug. It can cause a crash in the future.

Fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: type 'Null' is not a subtype of type 'RenderBox' in type cast. Error thrown .
       at _DropDownTextFieldState.build.<fn>.<fn>(dropdown_textfield.dart:561)
       at RenderTapRegionSurface.handleEvent(tap_region.dart:275)
       at GestureBinding.dispatchEvent(binding.dart:481)
       at RendererBinding.dispatchEvent(binding.dart:450)
       at GestureBinding._handlePointerEventImmediately(binding.dart:426)
       at GestureBinding.handlePointerEvent(binding.dart:389)
       at GestureBinding._flushPointerEventQueue(binding.dart:336)
       at GestureBinding._handlePointerDataPacket(binding.dart:305)