IE11, findParent fails with 'Unable to get property '__reactInternalInstance$...' of undefined or null reference

[Ragnaroek]

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

What is the current behavior?
Exception is thrown, rendering stops.

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/).
Doesn't seem to be determinstic, but it happens only in IE (at least in IE11).

What is the expected behavior?
Should not throw an exception and continue rendering.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
React 15.2.1, IE 11 on Windows 8.1

[Ragnaroek]

This PR tries to fix the symptoms: #8032

[aweary]

@Ragnaroek thanks for the report!

Doesn't seem to be determinstic, but it happens only in IE (at least in IE11).

Can you share a test case that reproduces it nondeterministically? Even if it isn't consistent, it's better than nothing. I would say fixing the symptoms and not the issue isn't a good idea here, as it may just hide a deeper issue or cause hard to debug problems somewhere else in the code path.

[Ragnaroek]

I agree that fixing the symptom this way was a bad idea.
As it turned out the problem was not React, but an exception in one of our promise handlers.

[aweary]

@Ragnaroek thanks for the update, glad you figured it out 👍!