TypeConverter not running for strings of type Object

[kpentaris]

When declaring a TypeConverter, it properly runs if the Java field is of type String but if it is of type Object in which case XStream puts the runtime type in a class attribute, the TypeConverter never runs.

The problem is in the MappedXMLStreamWriter.JSONPropertyObject class in the withProperty method as well as in MappedXMLStreamWriter.JSONPropertyString.
Current implementation:

Object value = property.getValue();
if (add && value instanceof String) {
  value = this.convention.convertToJSONPrimitive((String)value);
}

Suggested implementation idea (needs exception handling etc):

Object value = property.getValue();
if (add && value instanceof String) {
  value = this.convention.convertToJSONPrimitive((String)value);
} else if (add && value instanceof JSONObject && "string".equals(value.get("@class"))) {
  value.put("$",  this.convention.convertToJSONPrimitive((String)value.get("$")));
}