fix: return compound tag instead of end tag for empty Ops value

[PierreSchwang]

Overview

NbtOps returns a EndTag for the empty entry, which doesn't work with Lin (does make sense tbf) and fails when, for example, appending empty to a map. Switched to an empty compound tag which works and should work for other cases as well.

I don't really know under which circumstances this is actually used - possibly some Codec haven't been able to test.

Submitter Checklist

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