how to fix ! operator giving null value

Null operator issue flutter

got an issue where the app crash because of null value but when i be using the app for a while then add this and hot reload the app it works

'${( controller.currentWeatherData.main!.temp! - 273.15).round().toString()}\u2103',

couldn't tell how to fix it

tried using ? but have another bug

Text(
  '${(controller.currentWeatherData.main!.temp! - 273.15).round().toString()}\u2103',
  //  'round',
  style: Theme.of(context)
      .textTheme
      .headline2!
      .copyWith(
          fontSize:
              AppDime.md_14,
          // color:
          //     Colors.black45,
          fontFamily:
              'flutterfonts'),
),

You can do a null check first instead of using null-assert,

if(controller.currentWeatherData.main?.temp!=null) 
   Text( '${( controller.currentWeatherData.main!.temp - 273.15).round().toString()}\u2103',)
 else Text("Got null"),

Or just default value on case can be

'${((controller.currentWeatherData.main?.temp?? 0) - 273.15).round().toString()}\u2103'