Revert "chore(*): remove assign"

This reverts commit 1bc6951.

kong/db/dao/certificates.lua

@@ -60,6 +60,7 @@ function _Certificates:insert(cert, options)
     end
   end
 
+  cert.snis = nil
   cert, err, err_t = self.super.insert(self, cert, options)
   if not cert then
     return nil, err, err_t