Handle possible null return value for document.defaultValue

[ilias-t]

Do you want to request a feature or report a bug?
Bug, specific to react-dom.

What is the current behavior?
There is no null check for when document.defaultValue returns null as is specified as a possible return value in MDN docs.

In browsers, document.defaultView returns the window object associated with a document, or null if none is available.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:
Root cause seems pretty apparent in that we are not handling a possible null value. Will submit a fix shortly.

What is the expected behavior?
Error is not thrown if document.defaultValue returns null.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
Present on version 16.2.0.

[ilias-t]

Seems to have been addressed in #13650