Unhandled Exception: Null check operator used on a null value on Fitness.read

[FirdousNath]

Unhandled Exception: Null check operator used on a null value #0 Fitness.read.<anonymous closure> package:fitness/src/fitness.dart:43 #1 _rootRunUnary (dart:async/zone.dart:1362:47) #2 _CustomZone.runUnary (dart:async/zone.dart:1265:19)