bouncy-gpg BouncyCastle PGP GPG Java API NullPointerException when trying to encrypt with exported public key

I am trying to use the bouncy-gpg library with BouncyCastle to do PGP encryption in my Java programs. I keep getting the below NPE.
We had a shell script calling gpg on a Linux box and I wanted to move that logic into a Java app on Windows. I exported the public key from the keyring on Linux and try to use it on Windows but I always get the below error. I have tried all sorts of variations of different keys, formats and API options and I can't get encryption working with this one key. It worked OK with a key pair I generated myself.

Here is the method I wrote based on https://github.com/neuhalje/bouncy-gpg/blob/master/examples/encrypt/src/main/java/name/neuhalfen/projects/crypto/bouncycastle/openpgp/example/EncryptMain.java

  /**
   * Encypt the output file using gpg
   */
  public void encryptFile() {
    Path sourceFile = Paths.get(this.filePath());
    Path destFile = Paths.get(this.encryptedFilePath());
    try {
      BouncyGPG.registerProvider();

      int bufferSize = 8 * 1024;

      InMemoryKeyring keyringConfig = KeyringConfigs.forGpgExportedKeys(KeyringConfigCallbacks.withUnprotectedKeys());

      try {
      
 
 keyringConfig.addPublicKey(Files.readAllBytes(Paths.get("c:/path/to/my/exported.key"));
      } catch ( Exception e ) {
        throw new RuntimeException(e);
      }
      try (
          OutputStream fileOutput = Files.newOutputStream(destFile);
          BufferedOutputStream bufferedOut = new BufferedOutputStream(fileOutput, bufferSize);

          OutputStream outputStream = BouncyGPG
              .encryptToStream()
              .withConfig(keyringConfig)
              .withStrongAlgorithms()
              .toRecipient(recipient)
              .andDoNotSign()
              .binaryOutput()
              .andWriteTo(bufferedOut);

          InputStream is = Files.newInputStream(sourceFile)
          ) {
        Streams.pipeAll(is, outputStream);
      }
    } catch (Exception e) {
      throw new RuntimeException(e);
    }

And here is the stack trace of the exception:

Caused by: java.lang.NullPointerException
	at name.neuhalfen.projects.crypto.bouncycastle.openpgp.keys.generation.KeyFlag.extractPublicKeyFlags(KeyFlag.java:106)
	at name.neuhalfen.projects.crypto.bouncycastle.openpgp.keys.callbacks.Rfc4880KeySelectionStrategy.isEncryptionKey(Rfc4880KeySelectionStrategy.java:228)
	at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174)
	at java.util.ArrayList$Itr.forEachRemaining(ArrayList.java:891)
	at java.util.Collections$UnmodifiableCollection$1.forEachRemaining(Collections.java:1049)
	at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
	at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580)
	at java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:270)
	at java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1548)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.reduce(ReferencePipeline.java:479)
	at name.neuhalfen.projects.crypto.bouncycastle.openpgp.keys.callbacks.Rfc4880KeySelectionStrategy.selectPublicKey(Rfc4880KeySelectionStrategy.java:156)
	at name.neuhalfen.projects.crypto.bouncycastle.openpgp.BuildEncryptionOutputStreamAPI$WithAlgorithmSuiteImpl$ToImpl.extractValidKey(BuildEncryptionOutputStreamAPI.java:411)
	at name.neuhalfen.projects.crypto.bouncycastle.openpgp.BuildEncryptionOutputStreamAPI$WithAlgorithmSuiteImpl$ToImpl.toRecipient(BuildEncryptionOutputStreamAPI.java:431) ...

And the code block in bouncy-gpg where the NPE is occurring. The hashedSubPackets variable is null:

    while (directKeySignatures.hasNext()) {
      final PGPSignature signature = directKeySignatures.next();
      final PGPSignatureSubpacketVector hashedSubPackets = signature.getHashedSubPackets();

      final int keyFlags = hashedSubPackets.getKeyFlags(); // <- NPE HERE
      aggregatedKeyFlags |= keyFlags;
    }

Thanks very much in advance for any help.

The latest bouncy-gpg source code with the fix for https://github.com/neuhalje/bouncy-gpg/issues/48 resolved this issue. I retried my encryption method with the exported public key and it worked.