NullPointerException on MultipartInputImpl.PartImpl::getBody with MultipartRelatedInput as type

@GET
@Path("test")
@Produces("multipart/mixed")
public Response test() {
  ...
  final MultipartOutput multipartOutput = new MultipartOutput();
  entities.stream().map(entity -> {
    MultipartRelatedOutput multipartRelatedOutput = new MultipartRelatedOutput();
    multipartRelatedOutput.addPart(entity, MediaType.APPLICATION_JSON_TYPE);
    return multipartRelatedOutput;
  }).forEach(multipartRelatedOutput -> 
    multipartOutput.addPart(multipartRelatedOutput, MediaType.valueOf("multipart/related"))
  );
  return Response.ok(multipartOutput, MediaType.valueOf("multipart/mixed")).build();
}

public void get()
{
  try (Response response = this.proxy.test();) {
    ...
    MultipartInput multipartInput = response.readEntity(MultipartInput.class);
    for (InputPart inputPart : multipartInput.getParts()) {
    try {
      MultipartRelatedInput relatedInput = inputPart.getBody(MultipartRelatedInput.class, null);
    } catch (IOException exception) {}
  }
}

Caused by: java.lang.NullPointerException
	at java.base/java.io.SequenceInputStream.peekNextStream(SequenceInputStream.java:104)
	at java.base/java.io.SequenceInputStream.nextStream(SequenceInputStream.java:97)
	at java.base/java.io.SequenceInputStream.read(SequenceInputStream.java:203)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.io.BufferedLineReaderInputStream.fillBuffer(BufferedLineReaderInputStream.java:94)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.io.MimeBoundaryInputStream.fillBuffer(MimeBoundaryInputStream.java:196)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.io.MimeBoundaryInputStream.<init>(MimeBoundaryInputStream.java:75)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.parser.MimeEntity.createMimeStream(MimeEntity.java:217)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.parser.MimeEntity.advance(MimeEntity.java:152)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.parser.MimeTokenStream.next(MimeTokenStream.java:356)
	at org.apache.james.mime4j@0.6//org.apache.james.mime4j.parser.MimeStreamParser.parse(MimeStreamParser.java:144)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartInputImpl$BinaryMessage.<init>(MultipartInputImpl.java:184)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartInputImpl$BinaryMessage.<init>(MultipartInputImpl.java:169)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartInputImpl.parse(MultipartInputImpl.java:235)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartRelatedInputImpl.parse(MultipartRelatedInputImpl.java:35)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartRelatedReader.readFrom(MultipartRelatedReader.java:49)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartRelatedReader.readFrom(MultipartRelatedReader.java:26)
	at org.jboss.resteasy.resteasy-multipart-provider@3.7.0.Final//org.jboss.resteasy.plugins.providers.multipart.MultipartInputImpl$PartImpl.getBody(MultipartInputImpl.java:344)