intensity normalization: fix providing a dataset url

tomwer/core/process/reconstruction/nabu/nabucommon.py

@@ -536,11 +536,14 @@ class _NabuBaseReconstructor:
                 config["preproc"]["sino_normalization_file"] = dataset_url.path()
         elif source is INormSource.DATASET:
             url = extra_infos["dataset_url"]
-            if not isinstance(url, DataUrl):
+            if isinstance(url, DataUrl):
+                config["preproc"]["sino_normalization_file"] = url.path()
+            elif isinstance(url, str):
+                config["preproc"]["sino_normalization_file"] = url
+            else:
                 raise TypeError(
-                    f"dataset_url is expected to be an instance of DataUrl. Not {type(url)}"
+                    f"dataset_url is expected to be an instance of DataUrl or str representing a DataUrl. Not {type(url)}"
                 )
-            config["preproc"]["sino_normalization_file"] = url.path()
         else:
             raise NotImplementedError(f"source type {source.value} is not handled")