We are going to start importing our old excel sheets into JIRA, and therefore I've tried out the csv importer. To my surprise, new issue types, users and other items were created automatically without any warning. As we already have a fully configured JIRA environment with everything setup, I don't want the importer to create anything new. If it needs to, it is because I've made a mistake in the csv file or the mapping.
How can I make sure that I get a warning/error message if the importer sees the need to add things to my JIRA setup?
I am afraid as it is that the JIRA setup will be corrupted by new additions by the importer.