code: public static CountProjection countDistinct(String relativePath) {
      return new CountProjection(
          new DistinctProjection(
              new PathProjection(relativePath, false, false)
          )
      );
    }
docs: <p>
  Creates a "count distinct" projection for the specified relative path.
  </p>
  
  <p>
  Calling the method is the same as manually chaining calls to {@link #count(Projection)},
  {@link #distinct(Projection)} and {@link #relativePath(String)}.
  </p>
  
  <p>
  The result of the query will always be a {@link Long}.
  </p>
  
  @param relativePath relative path
  @return new projection instance