I'm getting this error called The named parameter 'key' is required, but there's no corresponding argument. I'm developing a simple BMI calculator app using flutter, android studio. didn't understand about the error I'm new to flutter. can anyone tell me what to do about this error? followed up this youtube video and the code is here github.

import 'package:bmi_cal/constants/app_constants.dart';
import 'package:bmi_cal/widgets/left_bar.dart';
import 'package:bmi_cal/widgets/right_bar.dart';
import 'package:flutter/material.dart';

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State {
  TextEditingController _heightController = TextEditingController();
  TextEditingController _weightController = TextEditingController();
  double _bmiResult = 0;
  String _textResult = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(
            "BMI Calculator",
            style:
            TextStyle(color: accentHexColor, fontWeight: FontWeight.w300),
          ),
          backgroundColor: Colors.transparent,
          elevation: 0,
          centerTitle: true,
        ),
        backgroundColor: mainHexColor,
        body: SingleChildScrollView(
          child: Column(
            children: [
              SizedBox(
                height: 20,
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                  Container(
                    width: 130,
                    child: TextField(
                      controller: _heightController,
                      style: TextStyle(
                          fontSize: 42,
                          fontWeight: FontWeight.w300,
                          color: accentHexColor),
                      keyboardType: TextInputType.number,
                      decoration: InputDecoration(
                        border: InputBorder.none,
                        hintText: "Height",
                        hintStyle: TextStyle(
                            fontSize: 42,
                            fontWeight: FontWeight.w300,
                            color: Colors.white.withOpacity(.8)),
                      ),
                    ),
                  ),
                  Container(
                    width: 130,
                    child: TextField(
                      controller: _weightController,
                      textAlign: TextAlign.center,
                      style: TextStyle(
                          fontSize: 42,
                          fontWeight: FontWeight.w300,
                          color: accentHexColor),
                      keyboardType: TextInputType.number,
                      decoration: InputDecoration(
                        border: InputBorder.none,
                        hintText: "Weight",
                        hintStyle: TextStyle(
                            fontSize: 42,
                            fontWeight: FontWeight.w300,
                            color: Colors.white.withOpacity(.8)),
                      ),
                    ),
                  ),
                ],
              ),
              SizedBox(
                height: 30,
              ),
              GestureDetector(
                onTap: () {
                  double _h = double.parse(_heightController.text);
                  double _w = double.parse(_weightController.text);
                  setState(() {
                    _bmiResult = _w / (_h * _h);
                    if(_bmiResult > 25){
                      _textResult = "You\'re over weight";
                    } else if(_bmiResult >= 18.5 && _bmiResult <= 25){
                      _textResult = "You have normal weight";
                    }else{
                      _textResult = "You\'re under weight";
                    }
                  });
                },
                child: Container(
                  child: Text(
                    "Calculate",
                    style: TextStyle(
                        fontSize: 22,
                        fontWeight: FontWeight.bold,
                        color: accentHexColor),
                  ),
                ),
              ),
              SizedBox(
                height: 50,
              ),
              Container(
                child: Text(
                  _bmiResult.toStringAsFixed(2),
                  style: TextStyle(fontSize: 90, color: accentHexColor),
                ),
              ),
              SizedBox(
                height: 30,
              ),
              Visibility(
                  visible: _textResult.isNotEmpty,
                  child: Container(
                    child: Text(
                      _textResult,
                      style: TextStyle(
                          fontSize: 32,
                          fontWeight: FontWeight.w400,
                          color: accentHexColor),
                    ),
                  )),
              SizedBox(height: 10,),
              LeftBar(barWidth: 40,),
              SizedBox(height: 20,),
              LeftBar(barWidth: 70),
              SizedBox(height: 20,),
              LeftBar(barWidth: 40,),
              SizedBox(height: 20,),
              RightBar(barWidth: 70),
              SizedBox(height: 50,),
              RightBar(barWidth: 70),
            ],
          ),
        ));
  }
}

main.dart

import 'package:bmi_cal/screens/home.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'BMI calculator',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.yellow,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: HomeScreen(),
    );
  }
}