public static List<String> getPropertyNames(String subdomain, String parent) {
        final MUCServiceProperties props = propertyMaps.computeIfAbsent( subdomain, MUCServiceProperties::new );
        return new ArrayList<>(props.getChildrenNames(parent));
    }
Return all immediate children property names of a parent Jive property as a list of strings,
or an empty list if there are no children. For example, given
the properties {@code X.Y.A}, {@code X.Y.B}, {@code X.Y.C} and {@code X.Y.C.D}, then
the immediate child properties of {@code X.Y} are {@code A}, {@code B}, and
{@code C} ({@code C.D} would not be returned using this method).<p>

@param subdomain the subdomain of the service to retrieve a property from
@param parent the root "node" of the properties to retrieve
@return a List of all immediate children property names (Strings).
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/MUCPersistenceManager.java