HandleStartObject.cs

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

    if (state.Current.IsProcessingEnumerable())
    {
        // A nested object within an enumerable.
        Type objType = state.Current.GetElementType();
        state.Push();
        state.Current.Initialize(objType, options);
    }
    else if (state.Current.JsonPropertyInfo != null)
    {
        // Nested object.
        Type objType = state.Current.JsonPropertyInfo.RuntimePropertyType;
        state.Push();
        state.Current.Initialize(objType, options);
    }

    JsonClassInfo classInfo = state.Current.JsonClassInfo;

    if (state.Current.IsProcessingObject(ClassType.Dictionary))
    {
        object value = ReadStackFrame.CreateDictionaryValue(ref state);

        // If value is not null, then we don't have a converter so apply the value.
        if (value != null)
        {
            state.Current.ReturnValue = value;
            state.Current.DetermineIfDictionaryCanBePopulated(state.Current.ReturnValue);
        }

        state.Current.CollectionPropertyInitialized = true;
    }
    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);
    }
}