title: Why do I get a huge grey circle in the background of scaffold?
body: <p>I have a PayBills() widget screen = that has 2 tabs which each display a separate tab dart file which I've specified, but I get a huge grey circle in the background of the first dart file and I get nothing in the second tab, but I don't know where the issue is.
  <a href="https://i.stack.imgur.com/yHzX7.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yHzX7.jpg" alt="enter image description here" /></a></p>
  <p><a href="https://i.stack.imgur.com/bjeGJ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bjeGJ.jpg" alt="enter image description here" /></a></p>
  <p>PayBills() widget screen code :</p>
  <pre><code>import 'package:flutter/material.dart';
  import '../../constans/constants.dart';
  import 'first_tab.dart';
  import 'second_tab.dart';
  
  class PayBills extends StatefulWidget {
    @override
    _PayBillsState createState() =&gt; _PayBillsState();
  }
  
  class _PayBillsState extends State&lt;PayBills&gt;
      with SingleTickerProviderStateMixin {
    TabController _controller;
    @override
    void initState() {
      super.initState();
      _controller = TabController(vsync: this, length: 2);
    }
  
    @override
    void dispose() {
      _controller.dispose();
      super.dispose();
    }
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
          backgroundColor: Colors.white,
          appBar: AppBar(
            backgroundColor: Colors.white,
            centerTitle: true,
            elevation: 0,
            title: Text(
              'تسديد فاتورة',
              style: TextStyle(
                color: leaderLogo,
                fontSize: 24,
                fontFamily: 'Calibri',
              ),
            ),
            bottom: TabBar(
              controller: _controller,
              tabs: [
                Tab(
                  child: Text(
                    'فواتير مستحقة',
                    style: TextStyle(
                      fontFamily: 'Calibri',
                      fontSize: 14,
                      color: Colors.black,
                    ),
                  ),
                ),
                Tab(
                  child: Text(
                    'فواتير مدفوعة',
                    style: TextStyle(
                      fontFamily: 'Calibri',
                      fontSize: 14,
                      color: Colors.black,
                    ),
                  ),
                ),
              ],
            ),
          ),
          body: TabBarView(
            controller: _controller,
            children: [
              PayBillsList(),
              SecondTab(),
            ],
          ));
    }
  }
  </code></pre>
  <p>first_tab widget code :</p>
  <pre><code>import 'package:flutter/material.dart';
  import '../../constans/constants.dart';
  
  class BillDetails extends StatelessWidget {
    final String billName;
    final String billImage;
    final String billDate;
  
    const BillDetails({Key key, this.billName, this.billImage, this.billDate})
        : super(key: key);
  
    @override
    Widget build(BuildContext context) {
      return Container(
          margin: EdgeInsets.only(
            top: 20,
            right: 5,
            left: 5,
          ),
          width: 378,
          height: 93,
          decoration: BoxDecoration(
            border: Border.all(
              color: Colors.grey,
            ),
            borderRadius: BorderRadius.circular(5),
          ),
          child: ListTile(
            leading: CircleAvatar(
              backgroundImage: AssetImage(billImage),
              backgroundColor: Colors.white,
            ),
            title: Text(
              billName,
              style: TextStyle(
                fontFamily: 'Calibri',
                fontSize: 16,
                color: Colors.black,
              ),
            ),
            subtitle: Text(
              billDate,
              style: TextStyle(
                fontFamily: 'Calibri',
                fontSize: 12,
                color: Colors.black,
              ),
            ),
            trailing: RaisedButton(
              color: raisedButtonColor,
              onPressed: () {},
              child: Text(
                &quot;دفع&quot;,
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
          ));
    }
  }
  
  class PayBillsList extends StatelessWidget {
    final List&lt;BillDetails&gt; billsList = [
      BillDetails(
        billName: 'فاتورة كهرباء',
        billImage: 'assets/images/electricity.png',
        billDate: '30 / 4 / 2020',
      ),
      BillDetails(
        billName: 'فاتورة مياه',
        billImage: 'assets/images/water.png',
        billDate: '30 / 4 / 2020',
      ),
    ];
  
    @override
    Widget build(BuildContext context) {
      return Container(
        width: 378,
        height: 93,
        decoration: BoxDecoration(
          border: Border.all(
            width: 1,
            color: Colors.grey,
          ),
          shape: BoxShape.circle,
        ),
        child: ListView.builder(
          itemBuilder: (context, index) {
            return BillDetails(
              billName: billsList.elementAt(index).billName,
              billImage: billsList.elementAt(index).billImage,
              billDate: billsList.elementAt(index).billDate,
            );
          },
          shrinkWrap: true,
          itemCount: billsList.length,
          scrollDirection: Axis.vertical,
        ),
      );
    }
  }
  
  class PayButton extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return ButtonTheme(
        minWidth: 20,
        height: 20,
        child: RaisedButton(
          onPressed: () {},
          color: raisedButtonColor,
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(10.0),
          ),
          child: Center(
            child: Text(
                //Login button text properties
                'دفع',
                style: TextStyle(
                  color: Colors.white,
                  fontSize: 18,
                  fontFamily: 'Calibri',
                )),
          ),
        ),
      );
    }
  }
  </code></pre>