[Minor] Try to stringify meta headers

Issue: #5237

diff --git a/src/plugins/lua/metadata_exporter.lua b/src/plugins/lua/metadata_exporter.lua
index e97dc8664d9fb90fe85c778900fc909a47267e86..de27a64aa59f21d6d2a3d15024efde6163fb3c0b 100644 (file)
--- a/src/plugins/lua/metadata_exporter.lua
+++ b/src/plugins/lua/metadata_exporter.lua
@@ -325,7 +325,7 @@ local pushers = {
         if type(v) == 'table' then
           hdrs[pfx .. k] = ucl.to_format(v, 'json-compact')
         else
-          hdrs[pfx .. k] = rspamd_util.mime_header_encode(v)
+          hdrs[pfx .. k] = rspamd_util.mime_header_encode(tostring(v) or '')
         end
       end
     end