我正在创建一个自定义的MaterialColor对象，但它抛出了这个错误。

• colors.dart*（我在这里创建MaterialColor对象）

import 'package:flutter/material.dart';

class JarsColors {
  static const MaterialColor palette = MaterialColor(
    0xFF276678,
    <int, Color> {
      0: Color(0xFFF6F5F5),
      100: Color(0xFFD3E0EA),
      400: Color(0xFF1687A7),
      500: Color(0xFF276678),
    }
  );
}

• 主.dart*

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: JarsColors.palette,
      ),
      home: JarsHome(title: 'Hello'),
    );
  }
}

错误输出：

The following _CastError was thrown building MyApp(dirty):
Null check operator used on a null value

The relevant error-causing widget was
MyApp
When the exception was thrown, this was the stack
#0      new ThemeData
#1      MyApp.build
#2      StatelessElement.build
#3      ComponentElement.performRebuild
#4      Element.rebuild

flutter doctor输出

λ flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 2.0.3, on Microsoft Windows [Version 10.0.19042.928], locale en-US)
[√] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
[√] Chrome - develop for the web
[√] Android Studio (version 4.1.0)
[√] VS Code (version 1.55.2)
[√] Connected device (3 available)

• No issues found!