value not present vs null

[m-mohr]

From experience in STAC and openEO, it seems some implementations/programming languages have a hard time to distinguish between "not present" and "null". Specifying different meanings for null and not present as for crs (unknown / CRS:84) might be a bad idea. Therefore, I'm putting out for discussion whether it's a good idea to do this and maybe instead use "unknown" as string or so instead of null?

[jorisvandenbossche]

I don't have a strong opinion about how we exactly represent this, except for that I want there is some way to indicate that the CRS is unknown.

In Python, it's very easy/natural to use null/None, so I can't judge about the difficulties it gives. Changing it to use "unknown" is not forward compatible (older readers will fail on files with this new value)

[m-mohr]

Closing, didn't seem overly relevant to implementors yet.