JSON Patch diffing fails due to ObjectMapper?

    public Map<String, String> fieldAndValueMap(Class<?> type, Object obj) throws ReflectiveOperationException {
        Map<String, String> result = new HashMap<>();
        for (Field field : type.getDeclaredFields()) {
            field.setAccessible(true);
            if (isWrapperType(field.getType())) {
                String value = nonNull(field.get(obj)) ? field.get(obj).toString() : "null";
                result.put(type.getSimpleName() + "." + field.getName(), value);
            } else {
                String getMethod = "get" + Character.toUpperCase(field.getName().charAt(0)) + field.getName().substring(1);
                Method method = type.getMethod(getMethod);
                Object subObj = method.invoke(obj);
                if (nonNull(subObj)) {
                    result.putAll(fieldAndValueMap(field.getType(), subObj));
                }
            }
        }
        return result;
    }

    public boolean isWrapperType(Class<?> type) {
        return getWrapperTypes().contains(type);
    }

    private Set<Class<?>> getWrapperTypes() {
        Set<Class<?>> ret = new HashSet<>();
        ret.add(Boolean.class);
        ret.add(Character.class);
        ret.add(String.class);
        ret.add(Byte.class);
        ret.add(Short.class);
        ret.add(Integer.class);
        ret.add(Long.class);
        ret.add(Float.class);
        ret.add(Double.class);
        ret.add(Void.class);
        ret.add(BigDecimal.class);
        ret.add(LocalDate.class);
        ret.add(LocalDateTime.class);
        ret.add(LocalTime.class);
        ret.add(Date.class);
        return ret;
    }