Explicitly emit null instead of dropping from output

diff --git a/lualib/lua_mime.lua b/lualib/lua_mime.lua
index 575e9152c002e20483a78b21ac98deb341ee375f..80e1080b59b4fc215533e97e7b3800a3887f1be8 100644 (file)
--- a/lualib/lua_mime.lua
+++ b/lualib/lua_mime.lua
@@ -607,7 +607,7 @@ exports.message_to_ucl = function(task, stringify_content)
     from_ip = maybe_stringify_ip(task:get_from_ip()),
   }
   if not next(result.envelope) then
-    result.envelope = nil
+    result.envelope = ucl.null
   end
 
   local parts = task:get_parts() or E