/**
     * Constructs a {@code SuppressFilterElement} using regular expressions
     * as {@code String}s. These are internally compiled into {@code Pattern}
     * objects and passed to the main constructor.
     *
     * @param files   regular expression for names of filtered files.
     * @param checks  regular expression for filtered check classes.
     * @param message regular expression for messages.
     * @param modId   the id
     * @param lines   lines CSV values and ranges for line number filtering.
     * @param columns columns CSV values and ranges for column number filtering.
     */
    public SuppressFilterElement(String files, String checks, String message,
                                 String modId, String lines, String columns) {
        this(toPattern(files), toPattern(checks), toPattern(message),
                modId, lines, columns);
    }

    /**
     * Converts a string into a compiled {@code Pattern}, or returns {@code null}
     * if the input is {@code null}.
     *
     * @param regex the regular expression as a string, may be {@code null}.
     * @return the compiled {@code Pattern}, or {@code null} if input is {@code null}.
     */
    private static Pattern toPattern(String regex) {
        final Pattern result;
        if (regex != null) {
            result = Pattern.compile(regex);
        }
        else {
            result = null;
        }
        return result;
    }