NoMethodError in Shelf#editquiz

Showing /app/app/views/shelf/editquiz.html.erb where line #11 raised:

undefined method `html_safe' for nil:NilClass
Did you mean?  html_safe?
Extracted source (around line #11):
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<script type="text/javascript">
$(function() {
init('<%= shelf.name %>', '<%= shelf.quiz.html_safe %>', <%= shelf.use_iqauth.to_s == '1' ? true : false %>, '<%= Digest::MD5.hexdigest(shelf.password.to_s) %>');
});
</script>

Rails.root: /app

Application Trace | Framework Trace | Full Trace

Request

Parameters:

{"shelfname"=>"MGN"}

Response

Headers:

None