How to fix Exception with queryStringParameters?

I am trying to read GET request parameters:

I have an exception if there are no parameters.

event = objectMapper.readTree(input);
JsonNode queryParameterMap = event.findValue("queryStringParameters"); 

However, I have no exception if I use "queryParameters" instead of "queryStringParameters".

How could I return null with no exception if there are no parameters?

final String keyParameter = Optional.ofNullable(queryParameterMap)
                .map(mapNode -> mapNode.get("my_key").asText())
                .orElse(null);

It looks like Exception came from mapping stage.

final String keyParameter = Optional.ofNullable(queryParameterMap)
                .filter(s -> !s.isEmpty())
                .map(mapNode -> mapNode.get("my_key").asText())
                .orElse(null);