<% if policy(@resource_service.build_resource({})).new? %>
  <%= link_to t("helpers.submit.create", model: @resource_class.model_name.human), [:new, *@resource_parents, @resource_class.model_name.singular_route_key], class: "btn btn-default" %>
<% end %>

<% if policy(@resource_service.build_resource({})).new? %>
  <%= link_to t("helpers.submit.create", model: @resource_class.model_name.human), [:new, *@resource_parents, @resource_class.model_name.singular_route_key.to_sym], class: "btn btn-default" %>
<% end %>

Patch incompatible code with newest Rails release
Patch incompatible code with newest Rails release

The latest Rails Security patch requires that polymorphic paths be constructed with symbols, rather than keys https://github.com/rails/rails/issues/42157

Release info: 
https://weblog.rubyonrails.org/2021/3/26/marcel-upgrade-releases/