Fix default model so more useful error is displayed

janus_core/mlip_calculators.py

@@ -53,7 +53,7 @@ def choose_calculator(
         # `model_paths` is keyword for path to model, so take from kwargs if specified
         # Otherwise, take `model` if specified, then default to `None`, which will
         # raise a ValueError
-        kwargs.setdefault("model_paths", kwargs.pop("model", None))
+        kwargs.setdefault("model_paths", kwargs.pop("model", ""))
         kwargs.setdefault("default_dtype", "float64")
         calculator = MACECalculator(device=device, **kwargs)