Error happens during h1 {string-set: headline content(text);}, causing pagedjs chunker to crash.

Message:

Uncaught (in promise) TypeError: Cannot read property 'replace' of undefined
    at cleanPseudoContent (paged.polyfill.js:29120)
    at StringSets.afterPageLayout (paged.polyfill.js:29225)
    at paged.polyfill.js:360
    at Array.forEach (<anonymous>)
    at Hook.trigger (paged.polyfill.js:359)
    at Chunker.layout (paged.polyfill.js:2519)
    at async Chunker.renderAsync (paged.polyfill.js:2440)

Possible fix /Workaround:

function cleanPseudoContent(el, trim = "\"' ") {
>>		if(el == null) return;
		return el
			.replace(new RegExp(`^[${trim}]+`), "")
			.replace(new RegExp(`[${trim}]+$`), "")
			.replace(/["']/g, match => {
				return "\\" + match;
			})
			.replace(/[\n]/g, match => {
				return "\\00000A";
			});
	}