title: Aggregation $size: Issue when FieldPath field name contains a number in the path
body: <p>I’m trying to get the size of an array so that I can use the number that it returns in a for loop. I’m using mongodb compass. I’m trying to use something like the projection below where 0 is an object inside of path and “here” is an array with 2 items.</p>
  <pre><code>$project
  {
      “alias” : {$size : “$this.is.the.field.path.0.here”}
  }
  </code></pre>
  <p>However, this keeps returning an array size of 0. It works fine for field paths that don’t contain a number in their path but returns 0 if the path does contain a number. Is there a way to properly get the correct size of the array here[ ] which has a size of 2?</p>