diff --git a/navipy/database/__init__.py b/navipy/database/__init__.py
index e0faf1343d3821e1afe7d0b5fd76d8653fd6a1d8..ce50392ea5b53c09278410c6562e9e8af6ee3cd2 100644
--- a/navipy/database/__init__.py
+++ b/navipy/database/__init__.py
@@ -61,6 +61,7 @@ class DataBase():
               channels: list
         """
         self._logger = logging.getLogger('navipy')
+        self.__convention = None
         if not isinstance(filename, str):
             msg = 'filename should be a string'
             self._logger.exception(msg)