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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)

return (
          <div>
            <input
              type="text"
              ref={n => (this.a = n)}
              value={this.state.value}
              onChange={e => this.change(e.target.value)}
              onBlur={e => this.blur(e.target.value)}
            />
            <input type="text" ref={n => (this.b = n)} />
          </div>
        );
      }
    }
    const instance = ReactDOM.render(<ControlledInputs />, container);
    
    
    instance.a.focus();
    setUntrackedValue.call(instance.a, 'giraffe');
    
    
    dispatchEventOnNode(instance.a, 'input');
    dispatchEventOnNode(instance.a, 'blur');
    expect(instance.a.value).toBe('giraffe');
    expect(instance.switchedFocus).toBe(true);
  });
  it('should control values in reentrant events with different targets', () => {
    class ControlledInputs extends React.Component {