src/main/java/org/apereo/cas/security/RequestParameterPolicyEnforcementFilter.java
static Set<Character> parseCharactersToForbid(String paramValue) {

        final Set<Character> charactersToForbid = new HashSet<Character>();

        if (null == paramValue) {
            paramValue = DEFAULT_CHARACTERS_BLOCKED;
        }

        if ("none".equals(paramValue)) {
            return charactersToForbid;
        }

        final String[] tokens = paramValue.split("\\s+");

        if (0 == tokens.length) {
            FilterUtils.logException(LOGGER, new IllegalArgumentException("Expected tokens when parsing [" + paramValue + "] but found no tokens."
                    + " If you really want to configure no characters, use the magic value 'none'."));
        }

        for (final String token : tokens) {

            if (token.length() > 1) {
                FilterUtils.logException(LOGGER, new IllegalArgumentException("Expected tokens of length 1 but found [" + token + "] when " +
                        "parsing [" + paramValue + "]"));
            }

            final Character character = token.charAt(0);
            charactersToForbid.add(character);
        }

        return charactersToForbid;
    }
static Set<Character> parseCharactersToForbid(String paramValue) {

        final Set<Character> charactersToForbid = new HashSet<Character>();

        if (null == paramValue) {
            paramValue = DEFAULT_CHARACTERS_BLOCKED;
        }

        if ("none".equals(paramValue)) {
            return charactersToForbid;
        }

        final String[] tokens = paramValue.split("\\s+");

        if (0 == tokens.length) {
            FilterUtils.logException(LOGGER, new IllegalArgumentException("Expected tokens when parsing [" + paramValue + "] but found no tokens."
                    + " If you really want to configure no characters, use the magic value 'none'."));
        }

        for (final String token : tokens) {

            if (token.length() > 1) {
                FilterUtils.logException(LOGGER, new IllegalArgumentException("Expected tokens of length 1 but found [" + token + "] when " +
                        "parsing [" + paramValue + "]"));
            }

            final Character character = token.charAt(0);
            charactersToForbid.add(character);
        }

        return charactersToForbid;
    }
Parse a whitespace delimited set of Characters from a String.
<p>
If the String is null (init param was not set) default to DEFAULT_CHARACTERS_BLOCKED.
If the String is "none" parse to empty set meaning block no characters.
If the String is empty throw, to avoid configurer accidentally configuring not to block any characters.

@param paramValue value of the init param to parse
@return non-null Set of zero or more Characters to block