Steps to reproduce:

1. create a new network discovery rule via API:

   {
       "jsonrpc": "2.0",
       "method": "drule.create",
       "params": [
           {
               "name": "test",
               "iprange": "127.0.0.1",
               "dchecks": [
                   {
                       "type": 9,
                       "key_": "system.uname"
                   }
               ],
               "error": "error message"
           }
       ],
       "id": 2
   }

Result:
The request will be successfully executed, and a rule will be created with the "error" field filled.