title: ListView.builder gives error: RenderBox was not laid out
body: <p>My <code>listview.builder</code> gives me tons of Renderbox errors such as flutter: </p>
  
  <blockquote>
    <p>Another exception was thrown: RenderBox was not laid out: RenderViewport#fa71e NEEDS-LAYOUT NEEDS-PAINT </p>
  </blockquote>
  
  <p>And: </p>
  
  <blockquote>
    <p>NoSuchMethodError: The method '&lt;=' was called on null. </p>
  </blockquote>
  
  <p>I tried adding a padding but to no avail. I am running on Flutter version 1.3.10. </p>
  
  <p>What was initialised wrongly?</p>
  
  <pre><code>import 'package:flutter/material.dart';
  
  void main() =&gt; runApp(TodoList());
  
  class TodoList extends StatefulWidget {
    @override
    State&lt;StatefulWidget&gt; createState() {
      // TODO: implement createState
      return _TodoListState();
    }
  }
  
  var TaskTextField;
  List taskTextList = [];
  var TaskIsImportant = false;
  
  class _TodoListState extends State&lt;TodoList&gt; {
    @override
    Widget build(BuildContext context) {
      // TODO: implement build
      return MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: Text("To-Do List V2"),
          ),
          body: Column(
            children: &lt;Widget&gt;[
              Container(
                child: TextField(
                  decoration: InputDecoration(
                    hintText: "Enter title of task to be added"),
                  onChanged: (taskTextField) {
                    setState(() {
                      TaskTextField = taskTextField;
                      print(TaskTextField);
                    });
                  },
                ),
                margin: EdgeInsets.all(16.0),
              ),
              CheckboxListTile(
                title: Text("Important"),
                activeColor: Colors.blue,
                value: TaskIsImportant,
                onChanged: (val) {
                  setState(() {
                    TaskIsImportant = !TaskIsImportant;
                    print(TaskIsImportant);
                  });
                },
              ),
              Container(
                margin: EdgeInsetsDirectional.fromSTEB(118, 20, 118, 20),
                child: Row(
                  children: &lt;Widget&gt;[
                    RaisedButton(
                      child: Icon(Icons.add),
                      onPressed: () {
                        setState(() {
                          if (TaskIsImportant) {
                            taskTextList.add("❗️$TaskTextField");
                            //taskTitleList.add(TaskDetailField);
                          } else {
                            taskTextList.add(TaskTextField);
                            //taskTitleList.add(TaskDetailField);
                          }
                        });
                      },
                    ),
                    RaisedButton(
                      child: Icon(Icons.done_all),
                      onPressed: () {
                        setState(() {
                          taskTextList = [];
                        });
                      },
                    ),
                  ],
                ),
              ),
              ListView.builder(
                itemBuilder: (context, index) {
                  var title = taskTextList[index];
                  padding: EdgeInsets.all(16.0);
                  return ListView(
                    children: &lt;Widget&gt;[
                      Text(title),
                    ],
                  );
                },
              ),
            ],
          ),
        ),
      );
    }
  }
  </code></pre>