*/
  @CheckForNull
  static String emptyToNull(@CheckForNull String string) {
    return stringIsNullOrEmpty(string) ? null : string;
  }

  static CommonPattern compilePattern(String pattern) {
    Preconditions.checkNotNull(pattern);
    return patternCompiler.compile(pattern);
  }

  static boolean patternCompilerIsPcreLike() {
    return patternCompiler.isPcreLike();
  }

  private static PatternCompiler loadPatternCompiler() {