partial correction for persistence

IMPORTANT: This version neec top be checked for meb import as seems that the cooling and heating demand aren't imported properly.

hub/imports/results_factory.py

@@ -31,7 +31,7 @@ class ResultFactory:
     self._handler = '_' + handler.lower().replace(' ', '_')
     validate_import_export_type(ResultFactory, handler)
     self._city = city
-    self._base_path = base_path
+    self._base_path = Path(base_path)
     self._hp_model = hp_model
 
   def _sra(self):