I have this function and it returns an object because it has no ideas what the return could be. It could be in long, int, String, or Foo

@SuppressWarnings("unchecked")
public Optional<Object> getRequestByFieldName(String fieldName) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    Class<?> classA = instanceA.getClass();

    Method method = classA.getMethod("getAllFields");

    Object o =  method.invoke(instanceA);

    // I'm using protobuf to get the field value,
    // but a field could be missing because someone didn't send it
    // in that case I return an Optional Empty object
    Map<Descriptors.FieldDescriptor, Object> objectMap = (Map) o;

    Object fieldValue =  objectMap.entrySet().stream()
            .filter(fieldDescriptorObjectEntry -> {
                Descriptors.FieldDescriptor descriptor = fieldDescriptorObjectEntry.getKey();
                return descriptor.getName().equals(fieldName);
            })
            .findFirst().map(fieldDescriptorObjectEntry -> fieldDescriptorObjectEntry.getValue())
            .orElse(Optional.empty());

    return Optional.of(fieldValue);
}

How do I use this function to assign a variable to an int, long or Foo? This is what I currently have:

long someUid = (long) getRequestByFieldName("some_uid").orElse(0);

However, I keep getting this error if the field was missing:

java.util.Optional cannot be cast to java.lang.Long