title: Can't include nested fields with spring data aggregation
body: <p>I have a problem with the inclusion and exclusion of nested fields in the aggregation.. I have a collection that contains nested objects, so when I try to build the query by including only some fields of nested objects it only works with the <strong>query</strong>, but it doesn't work with <strong>aggregation</strong></p>
  
  <p>This is a simple preview of my collection</p>
  
  <pre><code>{
      "id": "1234",
      "name": "place name",
      "address": {
          "city": "city name",
          "gov": "gov name",
          "country": "country name",
          "location": [0.0, 0.0],
          //some other data
      },
      //some other data
  }
  </code></pre>
  
  <p>when i configure my fields with <strong>query</strong> it works</p>
  
  <pre><code>query.fields().include("name").include("address.city").include("address.gov")
  </code></pre>
  
  <p>Also when I do it with aggregation using the shell it works</p>
  
  <pre><code>db.getCollection("places").aggregate([
      { $project: {
          "name": 1,
          "address.city": 1,
          "address.gov": 1
      } },
  ])
  </code></pre>
  
  <p>but it doesn't work with aggregation in spring</p>
  
  <pre><code>val aggregation = Aggregation.newAggregation(
          Aggregation.match(criteria)
          Aggregation.project().andInclude("name").andInclude("address.city").andInclude("address.gov")
  )
  </code></pre>
  
  <p>This aggregation with spring always returns address field as null, but when I put the "address" field without its nested fields the result will contain the full address object, not just its nested fields that I want to include.</p>
  
  <p>Can someone tell me how to fix that?</p>