Fix.

Did not handle the case on flower controller that the validation datasets maybe empty.

exareme2/controller/services/flower/controller.py

@@ -60,7 +60,7 @@ async def exec_algorithm(self, algorithm_name, algorithm_request_dto):
             ] = self.worker_landscape_aggregator.get_csv_paths_per_worker_id(
                 algorithm_request_dto.inputdata.data_model,
                 algorithm_request_dto.inputdata.datasets
-                + algorithm_request_dto.inputdata.validation_datasets,
+                + algorithm_request_dto.inputdata.validation_datasets if algorithm_request_dto.inputdata.validation_datasets else [],
             )
             workers_info = [
                 self.worker_landscape_aggregator.get_worker_info(worker_id)