BI Reporting filter values

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Hello,

I have a need to build complex audit reports. Where can I get a list of all the BI Reporting filter values? For example, I created a report to show me learning plans that had no mappings. After some research, I gathered  that my value has to be "equal to" SELECT_NULL (see picture). Is there a list of all the different types of values posted somewhere on MOS? Or is there an external forum someone could point me to?  Any info on the topic would be most helpful.

Thank you!