fix(startup): Button for startups url

- fix incorrect check for nil instead of empty

Author: drewhoffer

app/views/startups/show.html.erb

@@ -10,7 +10,7 @@
           <% end %>
         </div>
       </div>
-      <% unless @startup.url.nil? %>
+      <% unless (@startup.url.nil? || @startup.url.empty?) %>
         <%= link_to 'Visit Website', @startup.url, class: button_classes.render %>
       <% end %>
     </div>