CreatePageNestedDocumentsIT#createNestedDocumentsFromUI is flickering

java.lang.IllegalArgumentException: The executed javascript does not return a boolean value
	at org.xwiki.test.ui.XWikiWebDriver.lambda$waitUntilJavascriptCondition$8(XWikiWebDriver.java:605)
	at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:249)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilCondition(XWikiWebDriver.java:226)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilJavascriptCondition(XWikiWebDriver.java:597)
	at org.xwiki.test.ui.po.editor.EditPage.waitUntilPageJSIsLoaded(EditPage.java:292)
	at org.xwiki.test.ui.po.BasePage.<init>(BasePage.java:125)
	at org.xwiki.test.ui.po.editor.EditPage.<init>(EditPage.java:47)
	at org.xwiki.test.ui.po.CreatePagePage.createPage(CreatePagePage.java:120)
	at org.xwiki.flamingo.test.ui.CreatePageNestedDocumentsIT.createNestedDocumentsFromUI(CreatePageNestedDocumentsIT.java:123)

Current page URL is [http://localhost:8080/xwiki/bin/edit/A/B/WebHome?template=&parent=A.WebHome&title=B]