Allowing export projects even if any attachment doesn't exist in the storage

taiga/export_import/service.py

@@ -111,6 +111,7 @@ def render_project(project, outfile, chunk_size = 8190):
 
                     # We write the attached_files by chunks so the memory used is not increased
                     attachment_file = attachment.attached_file
+                    if default_storage.exists(attachment_file.name):
                         with default_storage.open(attachment_file.name) as f:
                             while True:
                                 bin_data = f.read(chunk_size)