added str_to_yes_no_null

smash/web/api_views/serialization_utils.py

@@ -25,6 +25,14 @@ def str_to_yes_no(val: str):
     else:
         return "NO"
 
+def str_to_yes_no_null(val: str):
+    if val is None:
+        return None
+    if val.lower() == 'true':
+        return "YES"
+    else:
+        return "NO"
+
 
 def virus_test_to_str(test, date):
     if test is None and date is not None: