Query for Custom Field

Question

I have a Custom field called Parent Link and I would like to query all those tickets that

* do not have it filled 
* have it with a content like SAGA

Currentluy I can write some JQL that returns tickets that have a Parent Link with one specific saga:

Project = EPI  and "Parent Link"="SAGA-45"

That works. Can you help me with the two other cases above?

improbable-marco · Answer

is not empty does not return any value either

Warren_mz9b4z · Answer

I'm not sure that you can do the second one, apart from is not EMPTY, which will be every issue which has a value in that field

improbable-marco · Answer

second question was filter all those that have content like SAGA like SAGA-45, SAGA-46 etc