docs: public static HttpString tryFromString(String string) {
          HttpString cached = Headers.fromCache(string);
          if(cached != null) {
              return cached;
          }
          final int len = string.length();
          final byte[] bytes = new byte[len];
          for (int i = 0; i < len; i++) {
              char c = string.charAt(i);
              if (c > 0xff) {
                  return null;
              }
              bytes[i] = (byte) c;
          }
          return new HttpString(bytes, string);
      }