What happened? (You can include a screenshot if it helps explain)

Tried running Everest without model in the config, which is marked as optional, it passed the original validation, but failed with:

Config validation error: Expected realizations when analysing data installation source

Realizations in model config should be a conlist (pydantic type) with min_length=1 and not defaulted. ModelConfig should not have a default value either.

What did you expect to happen?

Expected the config validation to tell me which keyword was missing, in this case:
Missing required model-> realizations

steps to reproduce

Remove the `model` section from for example minimal_config.yml and run the math func.

Environment where bug has been observed

• python 3.10
• python 3.11
• python 3.12
• macosx
• rhel7
• rhel8
• local queue
• lsf queue
• slurm queue
• openPBS queue