code: @Nonnull
      public Token expect(@Nonnull String expected) throws IOException {
          if (!hasNext()) {
              throw eof("Expected %s: Got end of file", expected);
          }
          lastToken = unreadToken;
          unreadToken = null;
          return lastToken;
      }
docs: Expect a new JSON token on the stream.
  
  @param expected Message to add to exception if there are no more JSON
  tokens on the stream.
  @return The next token.
  @throws IOException If unable to read from stream.