Change warning for <select value={null} /> to suggest an empty array rather than empty string

[ryb73]

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

What is the current behavior?
Setting the value to "" on a <select> with size > 3 does not deselect the currently selected option.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template: https://jsfiddle.net/reactjs/69z2wepo/).
JSFiddle: https://jsfiddle.net/rpbiwer/55jzq7dq/2/

What is the expected behavior?
After rendering a <select> with the value set to an empty string, I expect there to be no selection in the rendered select box. Mainly this expectation comes from this React warning when I use null instead of "":

Warning: `value` prop on `select` should not be null. Consider using the empty string to clear the component or `undefined` for uncontrolled components.

In the fiddle, if I change this line:

let newSelection = nowHidden ? "" : this.state.selected;

to

let newSelection = nowHidden ? undefined : this.state.selected;

I get the behavior I expect.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
I've gotten this with React 15.3.0 and whichever version is used in the fiddle. I don't know if it worked in previous versions.
This was tested using Chrome 56 on OS X.

[syranide]

"In my opinion" this is/was intended behavior. Empty string is a valid option value. Also, at least earlier, not all browsers support having no option selected which means that for these browsers the controlled input would be broken as it would have an option selected visually for the user but the value would still be null. But if that has changed and all browsers now do support it, then having a way to set "no value" would be a good idea yes.

[ryb73]

@syranide thanks for pointing that out. I wasn't aware of how the browsers handle this sort of thing. If what you say is still true, I'd change the request in this issue from "make "" work how I want it to" to "revise the misleading 'Consider using the empty string' error message".

[gaearon]

I think the correct fix here is to emit a different warning for select with props.multiple set to true. In this case we want to suggest an empty array rather than an empty string.

[nealwright]

Submitted a proposed fix: pull request #11141

[maecapozzi]

@Hendeca, it looks like your PR has been approved.

[gaearon]

Fixed in #11141.