code: public static StrMatcher charSetMatcher(final char... chars) {
          if (chars == null || chars.length == 0) {
              return NONE_MATCHER;
          }
          if (chars.length == 1) {
              return new CharMatcher(chars[0]);
          }
          return new CharSetMatcher(chars);
      }
docs: Constructor that creates a matcher from a set of characters.
  
  @param chars  the characters to match, null or empty matches nothing
  @return a new matcher for the given char[]