A Notebook throwing Exceptions leads to a blank Screen

[Andrea Amantini]

This is not always reproducible, but clerk/show!ing a notebook like

(ns repro 
  (:require [nexjtournal.clerk :as clerk]))

(clerk/html "x")

(/ 1 0)

causes the page to go blank with web console error

template.cljs:280 Uncaught Error: Assert failed: Invalid Hiccup form: [nil nil {:!expanded-at #object[reagent.ratom.RAtom {:val {:toc-open? true, :toc {}}}], :viewer nil, :path nil}]
 (in nextjournal$clerk$render$inspect_presented)
(valid-tag? tag)