title: Postman null value in optional string field
body: <p>I'm writing a POST request in Postman. There is an optional field, which can contain <code>null</code> or a date (a string value). So, I have this in my POST request body:</p>
  
  <pre><code>"paidOn": "{{date}}"
  </code></pre>
  
  <p>It works great with non-null values, obviously. But if I put <code>null</code> in the <code>paidOn</code> column, it ends up like a string <code>"null"</code>. If I put nothing, it ends up like an empty string <code>""</code>. In both cases, I get a 400 error.</p>
  
  <p>I tried another approach too:</p>
  
  <pre><code>"paidOn": {{date}}
  </code></pre>
  
  <p>This one works ok with empty fields, but doesn't when I have an actual date in it (like, <code>2020-04-13T14:39:52</code>) -> I get a 400 error.</p>
  
  <p>Does anyone know how I could work it out?</p>