Please include your configuration information, because that will affect whether my suggestion below applies to your question.
Please look into using Advanced Query capabilities within many grids in JDE. For null value, maybe try <1. You can use not equal to in the AQ or in the QBE line. For the greater/less combo you can use "between" in the AQ. Don't know about the third character one, though -- I don't think AQ can handle that one.
In case you haven't discovered it by now, you can search a grid for "not equal to x" by typing "!x" or "!=x" in the QBE line.
The advanced query search in Tools 9.1 allow you to search for "is null" or "is between" x and y.
Can't think of a way to search for the third character of a field.
Thank you for specifying the application and form. Could you please specify exactly what you're typing in the QBE line? Are you typing the words "EQUAL" and "CONTAINS", or typing something else?
Sounds like you have it solved my friend just be mindful of how you populate the QBE line to retrieve the expected results. And remember that sometimes you may need to populate a few alternatives to achieve success.