title: MongoDB query to replace NULL values
body: <p>I'm currently working with a MongoDB database and I have fields that have a value of NULL is there a way to run a query that will replace these NULL fields with a value of &quot;Missing&quot; instead?
  An example of the document is:</p>
  <pre><code>{
          &quot;_id&quot; : 1,
          &quot;Users&quot; : [
                  {
                          &quot;name&quot; : &quot;John Davies&quot;,
                          &quot;age&quot; : null,
                          &quot;place_of_birth&quot; : &quot;Cardigan&quot;
                  },
                  {
                          &quot;name&quot; : &quot;Edward Jones&quot;,
                          &quot;age&quot; : null,
                          &quot;place_of_birth&quot; : null
                  },
                  {
                          &quot;name&quot; : &quot;Daniel Rhys&quot;,
                          &quot;age&quot; : NumberLong(63),
                          &quot;place_of_birth&quot; : &quot;Cardigan&quot;
                  },
                  {
                          &quot;name&quot; : null,
                          &quot;age&quot; : NumberLong(61),
                          &quot;place_of_birth&quot; : &quot;Cardigan&quot;
                  },
                  {
                          &quot;name&quot; : &quot;John Davies &quot;,
                          &quot;age&quot; : null,
                          &quot;place_of_birth&quot; : &quot;Cardigan&quot;
                  }
          ]
  }
  </code></pre>