using System;

using System.Text.Json;

using System.Text.Json.Serialization.Metadata;

​

var jsonSerializerOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web)

{

    TypeInfoResolver = new DefaultJsonTypeInfoResolver

    {

        Modifiers = { ExcludeEmptyStrings }

    }

};

​

var testObj = new

{

    Name = "John",

    LastName = "Doe",

    MiddleName = ""

};

​

var json = JsonSerializer.Serialize(testObj, jsonSerializerOptions);

​

Console.WriteLine(json);

​

static void ExcludeEmptyStrings(JsonTypeInfo jsonTypeInfo)

{

    if (jsonTypeInfo.Kind != JsonTypeInfoKind.Object)

        return;

​

    foreach (JsonPropertyInfo jsonPropertyInfo in jsonTypeInfo.Properties)

    {

        if (jsonPropertyInfo.PropertyType == typeof(string))

        {

            jsonPropertyInfo.ShouldSerialize = static (obj, value) => 

                !string.IsNullOrEmpty((string)value);

        }

    }

}