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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.

controlled?: boolean,
    ...
  },
  ...
};
let didWarnValueDefaultValue = false;
let didWarnCheckedDefaultChecked = false;
let didWarnControlledToUncontrolled = false;
let didWarnUncontrolledToControlled = false;
function isControlled(props) {
  const usesChecked = props.type === 'checkbox' || props.type === 'radio';
  return usesChecked ? props.checked != null : props.value != null;
}
/**
 * Implements an <input> host component that allows setting these optional
 * props: `checked`, `value`, `defaultChecked`, and `defaultValue`.
 *
 * If `checked` or `value` are not supplied (or null/undefined), user actions
 * that affect the checked state or value will trigger updates to the element.
 *
 * If they are supplied (and not null/undefined), the rendered element will not
 * trigger updates to the element. Instead, the props must change in order for
 * the rendered element to be updated.
 *
 * The rendered element will be initialized as unchecked (or `defaultChecked`)
 * with an empty value (or `defaultValue`).
 *
 * See http:www.w3.org/TR/2012/WD-html5-20121025/the-input-element.html
 */
export function getHostProps(element: Element, props: Object) {