handle case where no window is given

lib/single-file/util/doc-helper.js

@@ -80,6 +80,14 @@ this.docHelper = this.docHelper || (() => {
 		let elementsInfo;
 		if (win && doc.body) {
 			elementsInfo = getElementsInfo(win, doc, doc.body, options);
+		} else {
+			elementsInfo = {
+				canvasData: [],
+				imageData: [],
+				postersData: [],
+				usedFonts: [],
+				shadowRootsData: []
+			};
 		}
 		saveInputValues(doc);
 		return {