code: public Set<OpenPgpV4Fingerprint> getFingerprintsOfKeysWithState(PGPPublicKeyRingCollection publicKeys,
                                                                      OpenPgpTrustStore.Trust trust)
              throws IOException {
          PGPPublicKeyRingCollection keys = getPublicKeysOfTrustState(publicKeys, trust);
          Set<OpenPgpV4Fingerprint> fingerprints = new HashSet<>();
  
          if (keys == null) {
              return fingerprints;
          }
  
          for (PGPPublicKeyRing ring : keys) {
              fingerprints.add(new OpenPgpV4Fingerprint(ring));
          }
  
          return fingerprints;
      }
docs: Return a {@link Set} of {@link OpenPgpV4Fingerprint}s of all keys in {@code publicKeys}, which are marked with the
  {@link OpenPgpTrustStore.Trust} of {@code trust}.
  
  @param publicKeys {@link PGPPublicKeyRingCollection} of keys which are iterated.
  @param trust {@link OpenPgpTrustStore.Trust} state.
  @return {@link Set} of fingerprints
  
  @throws IOException IO error