You probably have more than one page on your site. Therefore parameters
does not exist in the layout for every page nanoc processes. For some pages the element will be nil
and hence the error you get.
Perhaps you need to rethink how you want to use those parameters, or then you need a conditional in your layout to look for parameters
and only use them when they are present:
<% if @item[:parameters] %>
<%= @item[:parameters][:abc] %>
<% end %>