app/views/lacquers/_add_or_remove_from_collection.html.erb
<% if current_user %>
<% if current_user.lacquers.include? lacquer %>
<% user_lacquer = current_user.user_lacquers.find_by(lacquer: lacquer) %>
<%= render 'user_lacquers/remove_button', lacquer: lacquer, user_lacquer: user_lacquer %>
<% else %>
<%= render 'user_lacquers/add_button', lacquer: lacquer %>
<% end %>
<% end %>