[datamodule] Use train split if no validation split available

src/mednet/libs/common/data/datamodule.py

@@ -570,7 +570,14 @@ class ConcatDataModule(lightning.LightningDataModule):
             The list of validation dataset names.
         """
 
-        return ["validation"] + [
+        validation_split_name = "validation"
+        if "validation" not in self.splits.keys():
+            logger.warning(
+                "No split named 'validation', the training split will be used for validation instead."
+            )
+            validation_split_name = "train"
+
+        return [validation_split_name] + [
             k for k in self.splits.keys() if k.startswith("monitor-")
         ]