code: public static String reverse(final String str) {
          if (str == null) {
              return null;
          }
          return new StringBuilder(str).reverse().toString();
      }
docs: <p>Reverses a String as per {@link StringBuilder#reverse()}.</p>
  
  <p>A {@code null} String returns {@code null}.</p>
  
  <pre>
  StringUtils.reverse(null)  = null
  StringUtils.reverse("")    = ""
  StringUtils.reverse("bat") = "tab"
  </pre>
  
  @param str  the String to reverse, may be null
  @return the reversed String, {@code null} if null String input