Fix hyperparameter logging crash with missing config values (#19)

* fix: logging hyperparameters with missing config values

* chore: update changelog

CHANGELOG.md

@@ -58,6 +58,7 @@ Keep it human-readable, your future self will thank you!
  - Moved callbacks into folder to fascilitate future refactor
  - Adjusted PyPI release infrastructure to common ECMWF workflow
  - Bumped versions in Pre-commit hooks
+ - Fix crash when logging hyperparameters with missing values in the config
 
 ### Removed
  - Dependency on mlflow-export-import

src/anemoi/training/diagnostics/mlflow/logger.py

@@ -27,6 +27,7 @@
 from pytorch_lightning.utilities.rank_zero import rank_zero_only
 
 from anemoi.training.diagnostics.mlflow.auth import TokenAuth
+from anemoi.training.utils.jsonify import map_config_to_primitives
 
 if TYPE_CHECKING:
     from argparse import Namespace
@@ -454,6 +455,11 @@ def log_hyperparams(self, params: dict[str, Any] | Namespace) -> None:
         """Overwrite the log_hyperparams method to flatten config params using '.'."""
         if self._flag_log_hparams:
             params = _convert_params(params)
+
+            # this is needed to resolve optional missing config values to a string, instead of raising a missing error
+            if config := params.get("config"):
+                params["config"] = map_config_to_primitives(config)
+
             params = _flatten_dict(params, delimiter=".")  # Flatten dict with '.' to not break API queries
             params = self._clean_params(params)