How do I exclude records based on the presence of a certain field (like the equivalent of SQL's [fieldname] Is Null)?

Example:

• Results for Closed questions include field closed_date=1234567890.

• Results for Open questions do not include this field as a Null as I would expect.

Is there a parameter I can add to the URL to exclude questions that have the field?

The only information I could find was from the documentation:

Absent Fields

_{To save space, the API does not return null values, instead opting to exclude the field altogether in the returned JSON. Fields that are not always guaranteed to be set (closed_date on question objects for example) are indicated in the per-type documentation. (Source)}