code: public static String deleteWhitespace(final String str) {
          if (N.isNullOrEmpty(str)) {
              return str;
          }
  
          final char[] chars = getCharsForReadOnly(str);
          final char[] cbuf = new char[chars.length];
          int count = 0;
          for (int i = 0, len = chars.length; i < len; i++) {
              if (!Character.isWhitespace(chars[i])) {
                  cbuf[count++] = chars[i];
              }
          }
  
          return count == chars.length ? str : new String(cbuf, 0, count);
      }
docs: <p>
  Deletes all white spaces from a String as defined by
  {@link Character#isWhitespace(char)}.
  </p>
  
  <pre>
  N.deleteWhitespace(null)         = null
  N.deleteWhitespace("")           = ""
  N.deleteWhitespace("abc")        = "abc"
  N.deleteWhitespace("   ab  c  ") = "abc"
  </pre>
  
  @param str
  the String to delete whitespace from, may be null
  @return the String without whitespaces, {@code null} if null String input