title: Comparing Julia variable to `nothing` using !== or !=
body: <p>In some Julia code when can see conditional expression such as</p>
  
  <pre><code>if val !== nothing
      dosomething()
  end
  </code></pre>
  
  <p>where <code>val</code> is a variable of type <code>Union{Int,Nothing}</code></p>
  
  <p>What is the difference between conditons <code>val !== nothing</code> and <code>val != nothing</code>?</p>