title: ActiveRecord: Find where column is nil or empty array
body: <p>I have an array column in postgres and I want to find all the records where this column is either <code>nil</code> or <code>[]</code>. I can search one or the other fine but trying both fails.</p>
  
  <p>This is what I attempted</p>
  
  <pre><code>Model.where(column: [nil, []])
  </code></pre>
  
  <p>But I get the error </p>
  
  <pre><code>ActiveRecord::StatementInvalid (PG::InvalidTextRepresentation: ERROR:  malformed array literal: "{NULL,{}}")
  DETAIL:  Unexpected "{" character.
  </code></pre>