React 0.14.7: `<option value="">empty</option>` emits empty string on change
http://jsbin.com/pisita/10/edit?html,js,console,output
React 15.0.0-rc.1`<option value="">empty</option>` emits string with value "empty" on change
http://jsbin.com/bemaze/12/edit?html,js,console,output
This is because React 15.0.0-rc.1 cuts off `value=""` from option tag

!didWarnValueDefaultValue
      ) {
        warning(
          false,
          '%s contains an input of type %s with both value and defaultValue props. ' +
          'Input elements must be either controlled or uncontrolled ' +
          '(specify either the value prop, or the defaultValue prop, but not ' +
          'both). Decide between using a controlled or uncontrolled input ' +
          'element and remove one of these props. More info: ' +
          'https://fb.me/react-controlled-components',
          owner && owner.getName() || 'A component',
          props.type
        );
        didWarnValueDefaultValue = true;
      }
      warnIfValueIsNull(props);
    }
    var defaultValue = props.defaultValue;
    inst._wrapperState = {
      initialChecked: props.defaultChecked || false,
      initialValue: defaultValue != null ? defaultValue : null,
      listeners: null,
      onChange: _handleChange.bind(inst),
    };
    if (__DEV__) {
      inst._wrapperState.controlled = props.checked !== undefined || props.value !== undefined;
    }
  },
  updateWrapper: function(inst) {
    var props = inst._currentElement.props;