Client Exception

My application is displaying a client exception.
Can you advise how to debug this?

Mon Mar 05 13:52:30 GMT-800 2018 com.vaadin.client.communication.MessageHandler
SEVERE: Error sending hierarchy change events
com.google.gwt.event.shared.UmbrellaException: Exception caught: (TypeError) : Cannot read property ‘removeChild’ of null
at Unknown.Hg(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.et(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.new gt(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Fs(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.uzb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Hzb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.EKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.zKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.fKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.cMb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.it(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.vt(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eval(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Uh(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Xh(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eval(com.adva.nlms.wfe.ui.WebUI-0.js)
Caused by: com.google.gwt.core.client.JavaScriptException: (TypeError) : Cannot read property ‘removeChild’ of null
at Unknown.hj(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.zkb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.u$c(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Mxb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Os(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Fs(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.uzb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Hzb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.EKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.zKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.fKb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.cMb(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.it(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.vt(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eval(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Uh(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.Xh(com.adva.nlms.wfe.ui.WebUI-0.js)
at Unknown.eval(com.adva.nlms.wfe.ui.WebUI-0.js)

That’s not really enough information to go on. Are you using some client-side add-on that could cause this exception?

-Olli