Non-zero exit code if lookup is undefined

[tilmanschweitzer]

I would be really great, it a lookup returns a non-zero exit code if the element is undefined. Currently one can not distinguish between an empty string and a undefined node or value

Example:
echo '{"name":"john","emptyName":""}' | json emptyName
echo '{"name":"john","emptyName":""}' | json notExistingName

Besides that your tool seems to be really great. I have a use case where I just want to check if json properties exist.