Ignore null properties during JSON serialization in C#

For instance, the following JSON includes a null value for the Description property:

{
  "Title": "Inception",
  "BoxOfficeMillions": 829.89,
  "Description": null
}

However, you can ignore null properties in two main ways:

1. Use a serialization setting to ignore all null properties.
2. Use an attribute to ignore a specific property when it's null.

In this article, I’ll show examples of how to ignore null properties with both System.Text.Json and Newtonsoft.

Ignore Null Properties with System.Text.Json

To ignore null properties, you can use the JsonIgnoreCondition.WhenWritingNull option in System.Text.Json.

Here’s how to apply it in two ways:

For All Properties

To ignore null properties globally, configure the JsonSerializerOptions.DefaultIgnoreCondition to JsonIgnoreCondition.WhenWritingNull. This will apply to all properties.

using System.Text.Json;
using System.Text.Json.Serialization;

var movie = new Movie()
{
    Title = "Inception",
    BoxOfficeMillions = 829.89,
    Description = null
};

var jsonOptions = new JsonSerializerOptions() 
{ 
    WriteIndented = true,
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
};

var json = JsonSerializer.Serialize(movie, jsonOptions);
Console.WriteLine(json);

Output:

{
  "Title": "Inception",
  "BoxOfficeMillions": 829.89
}

For Specific Properties

If you only want to ignore a specific property when it's null, you can apply the JsonIgnore attribute with JsonIgnoreCondition.WhenWritingNull.

using System.Text.Json.Serialization;

public class Movie
{
    public string Title { get; set; }
    public decimal BoxOfficeMillions { get; set; }

    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public string? Description { get; set; }
}

In this example, only the Description property is ignored if it is null, while other properties are serialized normally.

WhenWritingNull vs WhenWritingDefault

• WhenWritingNull ignores properties with null values.
• WhenWritingDefault ignores both null properties and properties with their default values (like 0 for integers, false for booleans).

Here’s an example where WhenWritingDefault is used:

var book = new Book()
{
    Title = "Atomic Habits",
    Pages = 0,  // int (default value)
    Author = null // string (null value)
};

var jsonOptions = new JsonSerializerOptions() 
{ 
    WriteIndented = true,
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
};

var json = JsonSerializer.Serialize(book, jsonOptions);
Console.WriteLine(json);

Output:

{
  "Title": "Atomic Habits"
}

Note that both null properties and properties with default values are omitted.

Ignore Null Properties with Newtonsoft

For those using Newtonsoft.Json, you can use NullValueHandling.Ignore to ignore null properties. This can be applied globally or on specific properties.

For All Properties

To ignore all null properties globally, use the JsonSerializerSettings.NullValueHandling setting:

using Newtonsoft.Json;

var book = new Book()
{
    Title = "Atomic Habits",
    Pages = null
};

var jsonSettings = new JsonSerializerSettings()
{
    Formatting = Formatting.Indented,
    NullValueHandling = NullValueHandling.Ignore
};

var json = JsonConvert.SerializeObject(book, jsonSettings);
Console.WriteLine(json);

Output:

{
  "Title": "Atomic Habits"
}

For Specific Properties

To ignore a specific property when it's null, use the JsonProperty attribute with NullValueHandling.Ignore:

using Newtonsoft.Json;

public class Book
{
    public string Title { get; set; }

    [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
    public int? Pages { get; set; }
}

In this case, if Pages is null, it will not be included in the serialized JSON, but other properties will still be serialized.