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

if (children != null) {
      if (__DEV__) {
        warning(
          false,
          'Use the `defaultValue` or `value` props instead of setting ' +
          'children on <textarea>.'
        );
      }
      invariant(
        defaultValue == null,
        'If you supply `defaultValue` on a <textarea>, do not pass children.'
      );
      if (Array.isArray(children)) {
        invariant(
          children.length <= 1,
          '<textarea> can only have at most one child.'
        );
        children = children[0];
      }
      defaultValue = '' + children;
    }
    if (defaultValue == null) {
      defaultValue = '';
    }
    var value = LinkedValueUtils.getValue(props);
    inst._wrapperState = {