ConvertUtils problem solved!
I got the solution to my ConvertUtils problem from the hibernate-devel mailing list. Thanks to Juozas Baliuka! Here's my new convert method:
public Object convert(Class type, Object value) { if (log.isDebugEnabled()) { log.debug("entering 'convert' method"); } // for a null value, return null if (value == null) { return null; } else if (value.getClass().isAssignableFrom(type)) { return value; } else if (ArrayList.class.isAssignableFrom(type) && (value instanceof Collection)) { return new ArrayList((Collection) value); // List, Set, Collection -> ArrayList } else if (type.isAssignableFrom(Collection.class) && (value instanceof Collection)) { try { //most of collections implement this constructor Constructor constructor = type.getConstructor(new Class[] { Collection.class }); return constructor.newInstance(new Object[] { value }); } catch (Exception e) { log.error(e); } } throw new ConversionException("Could not convert " + value.getClass().getName() + " to " + type.getName() + "!"); }