title: Get records where json column key is null
body: <p>I have table <code>users</code> with json column <code>details</code>.</p>
  
  <p>I want to fetch all user records where details["email"] is null or email key doesn't exist.</p>
  
  <p>This doesn't work:</p>
  
  <p><code>SELECT users.* FROM users where details-&gt;'email' IS NOT NULL;</code></p>
  
  <p><code>ERROR:  operator does not exist: json -&gt; boolean</code></p>