code: public ObjectNode toJson() {
  		ObjectMapper mapper = new ObjectMapper();
  		ObjectNode node = mapper.createObjectNode();
  		ObjectNode attributeNode = mapper.createObjectNode();
  
  		node.put(attribute.getCode(), attributeNode);
  		attributeNode.put("op", operation.getOp());
  
  		return node;
  	}
docs: Returns a JSON representation of this filter to send to the server. Used
  by the SDK internally.
  
  @return a JSON representation of this filter