Fixed multiword prediction + bug that made the code write empty predictions

combo/config/from_parameters.py

@@ -58,6 +58,8 @@ def serialize_single_value(value: Any, pass_down_parameter_names: List[str] = No
         return {k: serialize_single_value(v, pass_down_parameter_names) for k, v in value.items()}
     elif isinstance(value, int) or isinstance(value, float) or isinstance(value, str):
         return value
+    elif value is None:
+        return None
     else:
         return str(value)