NullReferences Exception

Question

I got this error when I tried to run the good which gives and object reference not to an instance of an object

 

this is the code

string responseString = reader.ReadToEnd();
dynamic jsonData = JsonConvert.DeserializeObject(responseString);
var results = new List<Result>();
foreach (var item in jsonData.items)
{
results.Add(new Result
{
Title = item.title,
Link = item.link,
Snippet = item.snippet,
});
}

please kindly help