fix

lib/dl_api_lib/dl_api_lib/dataset/base_wrapper.py

@@ -263,15 +263,14 @@ def get_backend_type(self) -> SourceBackendType:
         return self._capabilities.get_backend_type(role=self.resolve_role())
 
     def _reload_sources(self) -> None:
-        self._has_sources = bool(self._ds.get_single_data_source_id())
         # resolve database characteristics
         # never go to database from here --> only_cache=True
-        if self._has_sources:
+        if (source_id := self._ds.get_single_data_source_id()) is not None:
+            self._has_sources = True
             role = self.resolve_role()
             try:
                 backend_type = self._capabilities.get_backend_type(role=role)
                 dialect_name = resolve_dialect_name(backend_type=backend_type)
-                source_id = self._ds.get_single_data_source_id()
                 dsrc = self._get_data_source_strict(source_id=source_id, role=role)
                 db_info = dsrc.get_cached_db_info()
                 db_version = db_info.version
@@ -281,6 +280,8 @@ def _reload_sources(self) -> None:
                 )
             except ReferencedUSEntryNotFound:
                 self.dialect = D.DUMMY
+        else:
+            self._has_sources = False
 
         if self._query_spec is not None:
             self.load_exbuilders()