Merge pull request #1210 from cta-observatory/wrong_raise_error_path_…

…exists

Fix unsupported operand type in existing DL2 file

lstchain/scripts/lstchain_dl1_to_dl2.py

@@ -200,7 +200,7 @@ def apply_to_file(filename, models_dict, output_dir, config):
     output_file = output_dir.joinpath(filename.name.replace('dl1', 'dl2', 1))
 
     if output_file.exists():
-        raise IOError(output_file + ' exists, exiting.')
+        raise IOError(str(output_file) + ' exists, exiting.')
 
     dl1_keys = get_dataset_keys(filename)