@Override
    public String apply(String string) {
      try {
        return UCharacter.foldCase(string, true);
      } catch (NoClassDefFoundError e) {
        NoClassDefFoundError error =
            new NoClassDefFoundError(
                "PathNormalization.CASE_FOLD_UNICODE requires ICU4J. "
                    + "Did you forget to include it on your classpath?");
        error.initCause(e);
        throw error;
      }
    }
Unicode case folding for case insensitive paths. Requires ICU4J on the classpath.
jimfs/src/main/java/com/google/common/jimfs/PathNormalization.java