Sometimes when you’re writing ERB, you’ll have to output something like this:

<%= article.category.name %>

But if the category is not set, you’ll probably get an error page with a nasty backtrace of an exception, along with an error like:

undefined method 'name' for nilclass

There are a couple ways to avoid this. First, you can test if category is nil before outputting the value:

<% if not article.category.blank? -%>
<%= article.category.name %>
<% else -%>
No Category
<% end -%>

Another way that is a bit cleaner is to add a rescue statement to the end of your output:

<%= article.category.name rescue 'No Category' %>

Using rescue will only catch exceptions, and will not test if the name itself is nil or an empty string. So, use either one based on your situation.