Loop JSON objects may not always exist

Question

I have a complex JSON object I'm having difficulty with. The problem is that sometimes, a sub list of items within the JSON model may not exist for each element. Ie. completely missing.

The JSON objects vary, for the few elements returning everything, I can often get 2 or 3 complete returned items so I know my object model for at least some part, works but for example Name1 from the below model will return successfully. But then errors parsing Name2 . So I can't seem to loop through the entire list without an Exception.

"Object reference not set to an instance of an object"

I tried to wrap the outputs within Try Catch blocks however I am still returning an error.

Sample JSON with all use cases

[
  {
  "name": "Name1",
  "description": "",
  "location": "ANY",
  "inputs":       [
     {
        "name": "input1",
        "required": true,
        "description": "some short description"
     },
     {
        "name": "input2",
        "required": true,
        "description": "another short description"
     }
  ],
  "outputs":       [
     {
        "name": "output1",
        "required": false
     },
     {
        "name": "outpu2",
        "required": false
     }
  ]
 },
  {
   "name": "Name2",
   "description": "some long description",
   "location": "ANY",
   "inputs": [      {
        "name": "input1",
        "required": false,
        "description" : "some short description of the input"
  }]
  },
  {
     "name": "Name3",
     "description": "",
     "location": "ANY"
   }
 ]

My C# Definitions work for the first reference for this JSON object, however for "Name2 and "Name3" I am getting this "object reference not set to an instance of an object" error.

My C# Json Definitions

 public class inputParameters
{
    [JsonProperty("name")]
    public string inputName { get; set; }

    [JsonProperty("required")]
    public bool inputRequired {get; set;}

    [JsonProperty("description")]
    public string inputDescription {get; set;}
}
public class outputParameters
{
    public string outputName { get; set; }
    public bool outputRequired { get; set; }
}
public class JsonObject
{
    [JsonProperty("name")]
    public string ProcessName { get; set; }

    [JsonProperty("description")]
    public string ProcessDescription { get; set; }

    [JsonProperty("peerLocation")]
    public string PeerLocation { get; set; }

    public List<inputParameters> InputParameters { get; set; }
    public List<outputParameters> OutputParameters{ get; set; }
}

And my Deserializing object and loops

var Object = JsonConvert.DeserializeObject <List<JsonObject>>(txt);

            foreach (JsonObject JsonObject in Object)
            {
                Console.WriteLine("Process Name: " + JsonObject.ProcessName);
                Console.WriteLine("PeerLoacatoin: " + JsonObject.PeerLocation);
                Console.WriteLine("Process Description: " +JsonObject.ProcessDescription);


                foreach (var InputParams in JsonObject.InputParameters)
                {
                    try
                    {
                        Console.WriteLine("Input Name: " + InputParams.inputName);
                        Console.WriteLine("Input Required: " + InputParams.inputRequired);
                        Console.WriteLine("Input Description: " + InputParams.inputDescription);
                    }

                    catch(Exception) 
                    {
                        InputParams.inputName = "";
                        InputParams.inputRequired = false;
                        InputParams.inputDescription = "";
                    }

                }
                foreach (var OutputParams in JsonObject.OutputParameters)
                {
                    try
                    {
                        Console.WriteLine("Output Name: " + OutputParams.outputName);
                        Console.WriteLine("Output Required: " + OutputParams.outputRequired);
                    }
                    catch (Exception)
                    {
                        OutputParams.outputName = "";
                        OutputParams.outputRequired = false;
                    }
                }
                Console.WriteLine();

Answer 1

I would create a constructor which initializes all your List s to new List . That way you can safely iterate without getting null pointer exceptions.

class JsonObject
{
    public JsonObject()
    {
        InputParameters = new List<inputParameters>();
        OutputParameters = new List<outputParameters>();
    }
}