If file type is unknown, treat it as application/octet-stream

boards/utils.py

@@ -142,4 +142,8 b' def get_upload_filename(model_instance, '
 
 
 def get_file_mimetype(file) -> str:
-    return magic.from_buffer(file.chunks().__next__(), mime=True).decode()
+    type = magic.from_buffer(file.chunks().__next__(), mime=True)
+    if type is not None:
+        return type.decode()
+    else:
+        return 'application/octet-stream'