Customers are commonly finding the difference between the IS EMPTY and != options in JQL to be confusing.

For example, if I do a search for issues where AnimalField != Cat will return results where AnimalField is set to Dog, but not where that field is empty.

Essentially the != operator means this field has a value, but the value is not Cat.

Many customers find themselves expecting it to mean "Does not equal or is empty", they try to understand why this behaviour isn't working as expected and hit up the docs, which do say it, but kind of hidden away. Could we add a section to call this out a bit louder?

https://confluence.atlassian.com/display/JIRA/Advanced+Searching