Bug that prevents supporting trees trained with a custom objective function

[jamespinkerton]

Hi. I changed my objective function to be custom, and on compilation I guess this error:

File "/mnt/disks/condaman/mamba/lib/python3.12/site-packages/lleaves/compiler/ast/scanner.py", line 132, in _scan_block
raise RuntimeError(f"Missing non-nullable keys {missing_keys}")
RuntimeError: Missing non-nullable keys {'objective'}

Can we exclude this from the requirements?

Thanks