Removal of all null custom fields from curl command results?

[luke laney]

Hello all, I am trying to use a curl command to return info on a specified issues. When the json is returned, many of the custom fields are null. 

ex. " curl --user user:pass https://blahblah/rest/api/2/issue/issue-1234 "

When I try to append something like "?fields=notnull", the result does remove nulls, but the only things returned are id, key, self, and expand.

How would I alter my curl command to only return fields/custom fields that are not null?