When the selectLastEvent query is enabled on a trigger.get API call, triggers with no events return an empty array instead of a null value.

Steps to reproduce:

1. Make a trigger.get API call with selectLastEvent enabled. For example:

   {
     "method": "trigger.get",
     "params": {
       "selectLastEvent": "extended"
     },
     "auth": "xxx",
     "jsonrpc": "2.0",
     "id": 1
   }
   

Result:

{
  "jsonrpc": "2.0",
  "result": [
    {
      "triggerid": "1234",
      "lastEvent": []
    }
  ],
  "id": 1
}

Expected:

{
  "jsonrpc": "2.0",
  "result": [
    {
      "triggerid": "1234",
      "lastEvent": null
    }
  ],
  "id": 1
}