title: What value does ActiveRecords return when a column is NULL?
body: <p>I'm in a environment where I can't test it, and I don't find information or any example on internet.</p>
  
  <p>Let's say I have a statement like this:</p>
  
  <pre><code>ActiveRecord::Base.connection.select_values("select a from table_b where id = 'x'")
  </code></pre>
  
  <p>(I know that it's not recommended and it's better to use other ways to deal with the database)</p>
  
  <p>If some rows have the column 'a' as NULL, what do I have in ruby? "NULL", Nil or another thing?</p>