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

Bug? Mild DX improvement.

**What is the current behavior?**

Creating an input with an undefined or null value, then later passing a string value, triggers a warning about controlled inputs.

> A component is changing an uncontrolled input of type undefined to be controlled. Input elements should not switch from uncontrolled to controlled (or vice versa)

It's my experience in Reactiflux that this warning is unclear to developers with less familiarity with React, or at least with the "controlled" and "uncontrolled" terms.

ReactDOM.render(<input />, container);
    ReactDOM.unmountComponentAtNode(container);
    ReactDOM.render(<input value={undefined} />, container);
    ReactDOM.unmountComponentAtNode(container);
    ReactDOM.render(<input type="text" />, container);
    ReactDOM.unmountComponentAtNode(container);
    ReactDOM.render(<input type="text" value={undefined} />, container);
    ReactDOM.unmountComponentAtNode(container);
    ReactDOM.render(<input type="checkbox" />, container);
    ReactDOM.unmountComponentAtNode(container);
    ReactDOM.render(<input type="checkbox" checked={undefined} />, container);
  });
  it('should not warn with value and onInput handler', () => {
    ReactDOM.render(<input value="..." onInput={() => {}} />, container);
  });
  it('should properly control a value even if no event listener exists', () => {
    let node;
    expect(() => {
      node = ReactDOM.render(<input type="text" value="lion" />, container);
    }).toErrorDev(
      'Warning: You provided a `value` prop to a form field without an `onChange` handler.',
    );
    setUntrackedValue.call(node, 'giraffe');
    
    
    dispatchEventOnNode(node, 'input');
    expect(node.value).toBe('lion');
  });
  it('should control a value in reentrant events', () => {
    class ControlledInputs extends React.Component {