Properties must be a 'array' type, but the final value was: 'null' in C#

Issue

I'm sending a field of array in multipart/form-data form to server, but when I call the variable in that array, it gives me an error.

Code

MultipartFormDataContent multiContent = new MultipartFormDataContent();
multiContent.Headers.ContentType.MediaType = "multipart/form-data";

string email = "[email protected]";
string firstName = "Andrie";
string lastName = "Tarkovsky";

var fields = "[{\"propertyName\": \"email\", \"propertyValue\": " + email + ", \"propertyLabel\": \"Email\"}, {\"propertyName\": \"firstName\", \"propertyValue\": " + firstName + ", \"propertyLabel\": \"First Name\"}, {\"propertyName\": \"lastName\", \"propertyValue\": " + lastName + ", \"propertyLabel\": \"Last Name\"}]";

multiContent.Add(new StringContent(fields), "properties");

Error

"\"properties must be a `array` type, but the final value was: `null` (cast from the value `\\\"[{\\\"propertyName\\\": \\\"email\\\", \\\"propertyValue\\\": [email protected], \\\"propertyLabel\\\": \\\"Email\\\"}, {\\\"propertyName\\\": \\\"firstName\\\", \\\"propertyValue\\\": Andrie, \\\"propertyLabel\\\": \\\"First Name\\\"}, {\\\"propertyName\\\": \\\"lastName\\\", \\\"propertyValue\\\": Tarkovsky, \\\"propertyLabel\\\": \\\"Last Name\\\"}]\\\"`).\\n If \\\"null\\\" is intended as an empty value be sure to mark the schema as `.nullable()`\""

UPDATE

public class Item
{
    public string name { get; set; }
    public string value { get; set; }
}

Solution

With the help of @jimenemex and @colex-msft solution, I solved it.

public class Item
{
    public string name { get; set; }
    public string value { get; set; }
}

public class DynamicObject
{
    public string PropertyName { get; set; }
    public string PropertyValue { get; set; }
}

List<Item> Obj = new List<Item>();
List<DynamicObject> Objs = new List<DynamicObject>();

foreach (var p in value.ToList())
{
    Objs.Add(new DynamicObject { PropertyName = p.name, PropertyValue = p.value });
}

var json = JsonConvert.SerializeObject(Objs);

Answered By - Stavrogin