return string || "";
  }-*/;

  @JsMethod
  static native String emptyToNull(@Nullable String string) /*-{
    return string || null;
  }-*/;

  static CommonPattern compilePattern(String pattern) {
    throw new UnsupportedOperationException();
  }

  static boolean patternCompilerIsPcreLike() {
    throw new UnsupportedOperationException();
  }

  // Re-declare this as abstract to force subclasses to override.
  @Override
  public abstract String toString();

  public static CommonPattern compile(String pattern) {
    return Platform.compilePattern(pattern);
  }

  public static boolean isPcreLike() {
    return Platform.patternCompilerIsPcreLike();
  }

         * @param pattern the path pattern string from robots.txt (may contain * and $)
         */
        public PathPattern(final String pattern) {
            this.pattern = pattern;
            this.regexPattern = compilePattern(pattern);
            this.priorityLength = calculatePriorityLength(pattern);
        }

        /**
         * Compiles a robots.txt path pattern into a regular expression pattern.

  private static final class ContainsPatternFromStringPredicate extends ContainsPatternPredicate {

    ContainsPatternFromStringPredicate(String string) {
      super(Platform.compilePattern(string));
    }

    @Override
    public String toString() {
      return "Predicates.containsPattern(" + pattern.pattern() + ")";
    }