code: @Nonnull
      public Query addAttribute(@Nonnull QueryAttribute attribute) {
          attribute.setQuery(this);
          attributesByName.put(attribute.getName(), attribute);
          attributeNames = attributesByName.keySet().toArray(new String[0]);
  
          return this;
      }
docs: Add the given attribute to the list attributes of this query
  and maintains the reverse relation (see {@link org.jmxtrans.embedded.QueryAttribute#getQuery()}).
  
  @param attribute attribute to add
  @return this