Error: Cannot read property 'style' of null

[calebcordry]

About 12k errors in new canary on stackdriver. Sample stack trace:

Error: Cannot read property 'style' of null
at style (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/src/style.js:119)
at (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/src/style.js:157)
at (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/extensions/amp-lightbox-gallery/0.1/swipe-to-dismiss.js:252)
at adjustForSwipePosition_ (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/extensions/amp-lightbox-gallery/0.1/swipe-to-dismiss.js:383)
at (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/src/service/resources-impl.js:1032)
at (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/src/service/vsync-impl.js:459)
at callTaskNoInline (https://raw.githubusercontent.com/ampproject/amphtml/1905222334000/src/service/vsync-impl.js:417)

Looks to be amp-lightbox-gallery related.
cc/ @ampproject/wg-ui-and-a11y

[calebcordry]

go/ampe/COuC3YCVi7zk7wE

[sparhami]

Looks like there was a spike on Sunday in the error rate, but has been lower before/after. I can't reproduce this when loading the canary version. I'm not 100% sure what is going on here. Here are something I know:

The error is happening here, with swipeElement_ being null:

amphtml/extensions/amp-lightbox-gallery/0.1/swipe-to-dismiss.js

Line 252 in f7d6f31

setStyles(dev().assertElement(this.swipeElement_), {

This is set on the first touch (from touchstart) here:

amphtml/extensions/amp-lightbox-gallery/0.1/swipe-to-dismiss.js

Line 161 in f7d6f31

this.swipeElement_ = swipeElement;

via:

amphtml/extensions/amp-lightbox-gallery/0.1/amp-lightbox-gallery.js

Line 645 in f7d6f31

swipeElement: dev().assertElement(this.carousel_),

At that point, this.carousel_ cannot not be null, since it is initialized before the lightbox opens.

I refactored this logic, but the data flow should be the same. The one thing I did change was I made the function use an object parameter instead of simple arguments, but I can't imagine that has any effect.

The minified code looks something like:

                    a.Na.startSwipe({
                        swipeElement: a.I,
                        hiddenElement: c || b,
                        mask: a.aa,
                        overlay: a.T
                    })

and

        U.prototype.startSwipe = function(a) {
            var b = this
              , c = a.swipeElement
              , d = a.hiddenElement
              , e = a.mask
              , f = a.overlay;
            this.oa = c;
            this.Ba = d;
            this.aa = e;
            this.ja = f;
            this.Ea(function() {
                Ab(b)
            })
        }

It is a little odd that the object properties are not being renamed, but it seems to be fine.

[sparhami]

Reopening until we can confirm whether or not we fixed this.

[jridgewell]

This is still not fixed, and it's by far the biggest error report in production.

[dreamofabear]

As of writing, both this error and the attempted fix ("subsequent without first" error in #25375) are both present and firing at high volume in RTV 1911191835190. The latter is about half the volume of the first.

[Enriqe]

@ampproject/wg-ui-and-a11y Can you please reassign this issue? Seeing 8k occurrences in the current canary 2001251659540 in the last day.

[kristoferbaxter]

Assigning @wassgha to take a look.