@CanIgnoreReturnValue
    public Builder setClock(Clock clock) {
      if (clock == null) {
        throw new NullPointerException("clock cannot be null");
      }
      this.clock = clock;
      return this;
    }
Sets the clock used to verify timestamp claims.
java_src/src/main/java/com/google/crypto/tink/jwt/JwtValidator.java