fix(Field): fix the issue of checking empty value

[beizhedenglong]

Some values like number 0, false shouldn't be treated as empty value.

[beizhedenglong]

像 switch 这种组件设置了必选，就变成了只能选true，感觉不太合理，你们很依赖这个特性嘛？

test('use switch', async () => {
  const { wrapper, onSubmit, onFailed } = mountFormWithChild({
    template: '<van-switch v-model="value" />',
    data() {
      return { value: false };
    },
  });

  await submitForm(wrapper);
  expect(onFailed).toHaveBeenCalledWith({
    errors: [{ message: 'foo', name: 'A' }],
    values: { A: false },
  });

  wrapper.setData({ value: true });

  await submitForm(wrapper);
  expect(onSubmit).toHaveBeenCalledWith({ A: true });
});

[chenjiahan]

其他 UI 组件库是按照哪一种标准来的嘞？

[beizhedenglong]

其他的主流组件库一般都不会有这种设定的。感觉不太合理， 像0，false 不应该认为是空值，不知道对你们是不是故意为之，这个改动对你们有影响吗

[chenjiahan]

按照浏览器的原生行为，Checkbox 如果设置了 required，是必须要选中的。

如果不需要校验 Checkbox/Switch 的选中状态，可以不设置 required

[beizhedenglong]

这个地方数字0也是有问题的，比如 RadioGroup 有三个数字选项0,1,2，设了必填，0现在是选不了的，只能特殊处理

[chenjiahan]

数字 0 可以修复一下，没问题

[codecov-commenter]

Codecov Report

Merging #7050 into dev will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #7050      +/-   ##
==========================================
+ Coverage   91.26%   91.27%   +0.01%     
==========================================
  Files         176      177       +1     
  Lines        4741     4747       +6     
  Branches      279      284       +5     
==========================================
+ Hits         4327     4333       +6     
  Misses        378      378              
  Partials       36       36              

Impacted Files	Coverage Δ
src/field/index.js	99.47% <100.00%> (+<0.01%)	⬆️
src/tabs/index.js	81.08% <0.00%> (-1.42%)	⬇️
src/action-sheet/index.tsx	100.00% <0.00%> (ø)
src/utils/interceptor.ts	100.00% <0.00%> (ø)
src/tabbar/index.js	94.11% <0.00%> (+0.36%)	⬆️

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[chenjiahan]

👍👍 辛苦