Fixed attachment extension

boards/utils.py

@@ -128,8 +128,8 b' def validate_file_size(size: int):'
 
 def get_upload_filename(model_instance, old_filename):
     # TODO Use something other than random number in file name
-    if hasattr(model_instance, 'file_type'):
-        extension = model_instance.file_type
+    if hasattr(model_instance, 'mimetype'):
+        extension = model_instance.mimetype
     else:
         extension = old_filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
     new_name = '{}{}.{}'.format(