code: public void setExpirationTime(long expirationTime) {
      if (expirationTime == NO_EXPIRE) {
        updateExpirationTime(NO_EXPIRE);
      } else if (expirationTime < 0) {
        throw new IllegalArgumentException("invalid expiration time: " + expirationTime);
      } else {
        updateExpirationTime(expirationTime);
      }
    }
docs: Set the new expiration time in milliseconds. Can be {@link #NO_EXPIRE} if the entry
  shouldn't expire.
  
  @param expirationTime new expiration time