code: public <ResultT> ResultT findOne(final Bson filter, final Class<ResultT> resultClass) {
      return proxy.findOne(filter, resultClass);
    }
docs: Finds a document in the collection.
  
  @param filter      the query filter
  @param resultClass the class to decode each document into
  @param <ResultT>   the target document type of the iterable.
  @return  a task containing the result of the find one operation