HandleStartDictionary.cs

private static void HandleStartDictionary(JsonSerializerOptions options, ref ReadStack state)
{
    Debug.Assert(!state.Current.IsProcessingEnumerable());

    JsonPropertyInfo jsonPropertyInfo = state.Current.JsonPropertyInfo;
    if (jsonPropertyInfo == null)
    {
        jsonPropertyInfo = state.Current.JsonClassInfo.CreateRootProperty(options);
    }

    Debug.Assert(jsonPropertyInfo != null);

    // A nested object or dictionary so push new frame.
    if (state.Current.CollectionPropertyInitialized)
    {
        state.Push();
        state.Current.JsonClassInfo = jsonPropertyInfo.ElementClassInfo;
        state.Current.InitializeJsonPropertyInfo();
        state.Current.CollectionPropertyInitialized = true;

        JsonClassInfo classInfo = state.Current.JsonClassInfo;

        if (state.Current.IsProcessingDictionary())
        {
            object dictValue = ReadStackFrame.CreateDictionaryValue(ref state);

            // If value is not null, then we don't have a converter so apply the value.
            if (dictValue != null)
            {
                state.Current.ReturnValue = dictValue;
                state.Current.DetermineIfDictionaryCanBePopulated(state.Current.ReturnValue);
            }
        }
        else if (state.Current.IsProcessingObject(ClassType.Object))
        {
            if (classInfo.CreateObject is null)
            {
                if (classInfo.Type.IsInterface)
                {
                    ThrowHelper.ThrowNotSupportedException_DeserializePolymorphicInterface(classInfo.Type);
                }
                else
                {
                    ThrowHelper.ThrowNotSupportedException_DeserializeMissingParameterlessConstructor(classInfo.Type);
                }
            }

            state.Current.ReturnValue = classInfo.CreateObject();
        }
        else
        {
            ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(classInfo.Type);
        }

        return;
    }

    state.Current.CollectionPropertyInitialized = true;

    object value = ReadStackFrame.CreateDictionaryValue(ref state);
    if (value != null)
    {
        state.Current.DetermineIfDictionaryCanBePopulated(value);

        if (state.Current.ReturnValue != null)
        {
            state.Current.JsonPropertyInfo.SetValueAsObject(state.Current.ReturnValue, value);
        }
        else
        {
            // A dictionary is being returned directly, or a nested dictionary.
            state.Current.ReturnValue = value;
        }
    }
}