code: static void validateHeaderValue(CharSequence value) {
          if (value == null) {
              throw new NullPointerException("value");
          }
          for (int i = 0; i < value.length(); i ++) {
              char c = value.charAt(i);
              if (c == 0) {
                  throw new IllegalArgumentException(
                          "value contains null character: " + value);
              }
          }
      }
docs: Validate a SPDY header value. Does not validate max length.