private static boolean addCausalChain(Set<Throwable> seen, Throwable param) {
    // Declare a "true" local variable so that the Checker Framework will infer nullness.
    Throwable t = param;

    for (; t != null; t = t.getCause()) {
      boolean firstTimeSeen = seen.add(t);
      if (!firstTimeSeen) {
        /*