private static String[] arrayDifference(String[] allowed, String[] disallowed, String[] defaultItems) {
        List<String> allowL = new ArrayList<>(Arrays.asList(optionalVar(allowed, defaultItems)));
        List<String> disallowL = new ArrayList<>(Arrays.asList(optionalVar(disallowed, EMPTY)));
        allowL.removeAll(disallowL);
        return allowL.toArray(new String[allowL.size()]);
    }
List A - List B

@param allowed allowed items
@param disallowed disallowed items
@return allowed items minus disallowed items
gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/connectors/ssl/SSLSessionStrategyFactory.java