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**Do you want to request a *feature* or report a *bug*?**

Bug.

**What is the current behavior?**

Creating an `<input type='submit'` with `value={undefined}` results in a button with no text. https://codesandbox.io/s/nn7p94y3rl

The same behaviour can be seen with `type='reset'`

I have a PR open with a proposed fix. https://github.com/facebook/react/pull/12780

**What is the expected behavior?**

The input should use the browser's default value for the input (Submit for en, etc.).

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React 16.3.2. Chrome 66.0.3359.139. macOS 10.13.4. Works in React 15 (unsure of earlier versions)

render() {
        return (
          <div>
            <input
              ref="a"
              type="radio"
              name="fruit"
              checked={true}
              onChange={emptyFunction}
            />
            A
            <input ref="b" type="radio" name="fruit" onChange={emptyFunction} />
            B
            <form>
              <input
                ref="c"
                type="radio"
                name="fruit"
                defaultChecked={true}
                onChange={emptyFunction}
              />
            </form>