Bugfix: MetaDataInfo add_metadatum method now adds the metadatum with the correct name

bob/io/stream/metadata.py

@@ -319,7 +319,7 @@ class MetaDataInfo:
         """
         if metadatum_name in self._info.keys():
             raise KeyError("Metadatum with name " + metadatum_name + " already exists in the metadatum info!")
-        self._info["metadatum_name"] = properties if properties is not None else {}
+        self._info[metadatum_name] = properties if properties is not None else {}
 
     def has_info_value(self, info_name, info_value, metadatum_name=None):
         """Return a list of the metadatum that have the `info_name` property with the `info_value` value.