fix: default dir initialization (#33)

Co-authored-by: Pablo <pjestradac@gmail.com>

Author: PJEstrada

sdk/diffgram/core/core.py

@@ -318,17 +318,15 @@ def set_default_directory(self,
         """
         if directory_id:
             self.directory_id = directory_id
-        if directory:
+        if directory is not None:
             self.directory_id = directory.id
             self.default_directory = directory
-            
         if not hasattr(self, 'directory_list'):
             self.directory_list = self.directory.get_directory_list()
 
         self.session.headers.update(
             {'directory_id': str(self.directory_id)})
 
-
 # TODO review not using this pattern anymore
 
 setattr(Project, "get_label_file_dict", get_label_file_dict)