code: 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;
      }
docs: 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