add empty dicts for all missing datasets

src/fairchem/core/trainers/base_trainer.py

@@ -151,22 +151,26 @@ def __init__(
             )
 
         # Define datasets
-        # or {} in cases where "dataset": None is explicitly defined
         if isinstance(dataset, list):
             if len(dataset) > 0:
-                self.config["dataset"] = dataset[0] or {}
+                self.config["dataset"] = dataset[0]
             if len(dataset) > 1:
-                self.config["val_dataset"] = dataset[1] or {}
+                self.config["val_dataset"] = dataset[1]
             if len(dataset) > 2:
-                self.config["test_dataset"] = dataset[2] or {}
+                self.config["test_dataset"] = dataset[2]
         elif isinstance(dataset, dict):
+            # or {} in cases where "dataset": None is explicitly defined
             self.config["dataset"] = dataset.get("train", {}) or {}
             self.config["val_dataset"] = dataset.get("val", {}) or {}
             self.config["test_dataset"] = dataset.get("test", {}) or {}
             self.config["relax_dataset"] = dataset.get("relax", {}) or {}
         else:
             self.config["dataset"] = dataset or {}
-            self.config["val_dataset"], self.config["test_dataset"] = {}, {}
+
+        # add empty dicts for missing datasets
+        for dataset_name in ("val_dataset", "test_dataset", "relax_dataset"):
+            if dataset_name not in self.config:
+                self.config[dataset_name] = {}
 
         if not is_debug and distutils.is_master():
             os.makedirs(self.config["cmd"]["checkpoint_dir"], exist_ok=True)