JSON input - optional tags/elements

Is there a way to have optional tags in the 'JSON Input' step?

ex.
{"address":{"street":"123 Main St","unit":"1","city":"San Francisco","state":"CA"}}
I want to be able to extract unit if it is there and have unit set null or empty string if it is not there.

It appears that if the path is not found ($.address.unit) the step fails with "We can not find any data with path [$.address.unit]!".
Putting an error_handling step still generates the error halting the transformation.

Is there a way to specify a JSON schema that defines the field as optional? Does the 'JSON Input' step support this?
is in the JSON schema having a definition "unit":{"type":"string";"optional":"true"} .

I have JSON input in which almost everything is optional except a few key fields and don't want to have to separate check for
each field. Is there a recommended java pkg that can do this? (I guess I would have to use a 'Modified Java_Script Value' step as
a wrapper in this case).