I have a counter this is configured to display the number of certain Jira issues introduced since a certain date. The query that I use returns all the issues in question, and I have a visualization counter set up that displays the count of the number of rows.

It works great when the number of rows returned is at least 1. But when zero rows are returned, it just shows blank. Is there any way to get it to show 0 when 0 rows are returned?

Nice catch. This is a bug. You can work around it for now with a second query that COUNTs the rows returned from your base query.