JObject issue_model = JObject.FromObject(new
{
   labels = new[] { "import", "automation"}
}

string request_json = JsonConvert.SerializeObject(issue_model,
                  Newtonsoft.Json.Formatting.Indented,
                  new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });

list<string> lp_list = new list<string>();
   //lp_list contains a list of string values
   string[] lp_labels = lp_list.ToArray();
   JObject issue_model = JObject.FromObject(new
   {
      labels = jira_labels
   }

"labels": [
  [
    null,
    null
  ]
]