new ArrayList<X>

Collections.emptyList();

interface Configurable {
    List<String> getConfigurationList();
}

// class which doesn't have any configuration
class SimpleConfigurable extends Configurable {
    public List<String> getConfigurationList() { return Collections.emptyList(); }
}

/**
 * Returns the empty list (immutable).  This list is serializable.
 *
 * <p>This example illustrates the type-safe way to obtain an empty list:
 * <pre>
 *     List<String> s = Collections.emptyList();
 * </pre>
 * Implementation note:  Implementations of this method need not
 * create a separate <tt>List</tt> object for each call.   Using this
 * method is likely to have comparable cost to using the like-named
 * field.  (Unlike this method, the field does not provide type safety.)
 *
 * @see #EMPTY_LIST
 * @since 1.5
 */