System.Text.Json: Error while deserializing dictionary returned as empty array

Question

I can't seem to solve this one. All other questions i can find with the same issue are for Newtonsoft.Json.

I use an external provided json API which returns a dictionary. But if it's empty, they return an empty array:

With data:

"booking/index": {
   "key": {
         data...
          }
}

Without data:

"booking/index": []

So the System.json deserializer fails with this error (which is understandable):

System.Text.Json.JsonException: The JSON value could not be converted to System.Collections.Generic.Dictionary`2[System.String,checkfront_reports.Models.Api.BookingIndexIndexObj]. Path: $['booking/index'] | LineNumber: 0 | BytePositionInLine: 408.

For reference here is the call i make and the data model:

var bookingIndex = await httpClient.GetFromJsonAsync<BookingIndexObj>($"booking/index?start_date={startDate.ToString("yyyy-MM-dd")}&end_date={endDate.ToString("yyyy-MM-dd")}");

public class BookingIndexObj
{
    public BookingRequestObj Request { get; set; }

    [JsonPropertyName("booking/index")]
    public Dictionary<string, BookingIndexIndexObj> BookingIndex { get; set; }
}

public class BookingIndexIndexObj
{
    public string? Code { get; set; }

    [JsonPropertyName("status_id")]
    public string? StatusId { get; set; }
}

public class BookingRequestObj
{
    public int Page { get; set; }

    public int Pages { get; set; }
}

Answer 1

I am not sure at all if this is how we are supposed to do this, but at least it worked:

(Note that I simplified the example)

using System;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        var emptyJson = 
            """
{
    "values": []
}
""";
    
        var nonEmptyJson = 
            """
{
    "values": {
        "key1": "value1",
        "key2": "value2"
    }
}
""";
        
        var emptyResult = JsonSerializer.Deserialize<Model>(emptyJson);
        var nonEmptyResult = JsonSerializer.Deserialize<Model>(nonEmptyJson);
        
        emptyResult.Dump();
        nonEmptyResult.Dump();
    }
}

public class Model
{
    [JsonPropertyName("values")]
    [JsonConverter(typeof(MySpecialConverter))]
    public Dictionary<string,string> Values {get;set;} = new();
}

public class MySpecialConverter : JsonConverter<Dictionary<string,string>>
{
// Omitted writer for brevity. 
    public override void Write(Utf8JsonWriter writer,
            Dictionary<string,string> dictionaryValue,
            JsonSerializerOptions options) => throw new NotSupportedException();
            
    public override Dictionary<string,string> Read(ref Utf8JsonReader reader,
            Type typeToConvert,
            JsonSerializerOptions options)
            {
// Check for '"booking/index": []' - case:
                if (reader.TokenType == JsonTokenType.StartArray)
                {
                  reader.Read();
                  return new Dictionary<string,string>();
                }
// Otherwise pass-through to default converter.
                var converter = (JsonConverter<Dictionary<string,string>>)options.GetConverter(typeof(Dictionary<string,string>));
                return converter.Read(ref reader, typeToConvert, options);
            }
}

=> Fiddle: https://dotnetfiddle.net/J6NbVE

For your reference:
I based this upon this article: How to write custom converters for JSON serialization (marshalling) in .NET