When building and testing Okta Workflows, the Okta List Users with Search card (and similar actions for other connectors) returns users when the card is set to search for an empty value.

• Okta Workflows
• All Connectors

Okta Workflows specifically does not send values for empty fields in most contexts. This means, for example, that a List Users with Search card set to search for an empty First Name simply ignores that empty value and hits the /api/v1/users endpoint without any query for First Name. 

Okta core API documentation.

This is an intentional design decision. Workflows generally assume that empty values are to be ignored before performing API operations (specific actions that require this functionality are the exceptions).

A possible workaround, depending on the desired behavior, is to utilize the Custom API Action card for the required connector. If a query parameter is included as an empty value in the "Relative URL" field, Workflows will include it in the API request.

Okta always recommends testing the Workflows on a small subset of data and validating their behavior before turning them on in production or running them at full scale.