Parsing jakarta.mail Message using tech.blueglacier.email-mime-parser library

Question

I am connecting to the a Gmail account and I try to read the unseen email using Jakarta Mail API. I try to use the tech.blueglacier.email-mime-parser library which is based on org.apache.james.mime4j in order to parse the Message and get the content of the mail. See the code from bellow.

public void fetchMail() throws MessagingException {
    Folder folder = null;
    try (Store store = Session.getDefaultInstance(imapMailConfig.imapMailProperties()).getStore("imap")) {
        store.connect(imapMailConfig.imapMailProperties().getProperty("host"), username, password);
        folder = store.getFolder(mailFolder);
        folder.open(Folder.READ_ONLY);
        log.info("Folder opened"); 
        Message[] messages = folder.search(new FlagTerm(new Flags(Flags.Flag.SEEN), false));
        log.info("Messages count: {}", messages.length);
        ContentHandler contentHandler = new CustomContentHandler();

        MimeConfig mime4jParserConfig = MimeConfig.DEFAULT;
        BodyDescriptorBuilder bodyDescriptorBuilder = new DefaultBodyDescriptorBuilder();
        MimeStreamParser mime4jParser = new MimeStreamParser(mime4jParserConfig, DecodeMonitor.SILENT,bodyDescriptorBuilder);
        mime4jParser.setContentDecoding(true);
        mime4jParser.setContentHandler(contentHandler);
        for (Message message : messages) {
            // retrieve the content of the message as an InputStream
            InputStream inputStream = message.getInputStream();
            mime4jParser.parse(inputStream);
            Email email = ((CustomContentHandler) contentHandler).getEmail();

            List<Attachment> attachments = email.getAttachments();

            Attachment calendar = email.getCalendarBody();
            Attachment htmlBody = email.getHTMLEmailBody();
            Attachment plainText = email.getPlainTextEmailBody();

            String to = email.getToEmailHeaderValue();
            String cc = email.getCCEmailHeaderValue();
            String from = email.getFromEmailHeaderValue();
            log.info("from: {}", from);
            log.info("getEmailSubject: {}", email.getEmailSubject());
        }
        // close the store and folder objects
        store.close();
        log.info("Close store");
    } catch (Exception e) {
        log.error(e.getMessage(), e);
    } finally {
        if (folder != null && folder.isOpen()) {
            log.info("Close folder");
            folder.close(true);
        }
    }
}

is returning the following error:

Folder opened
Messages count: 2
tech.blueglacier.email.Email             : mime part received
tech.blueglacier.email.Email             : Email plain text body identified
from: null
getEmailSubject: null
tech.blueglacier.email.Email             : mime part received
null

java.util.EmptyStackException: null
at java.base/java.util.Stack.peek(Stack.java:101) \~\[na:na\]
at tech.blueglacier.email.Email.addPlainTextEmailBody(Email.java:202) \~\[email-mime-parser-1.0.5.jar:na\]
at tech.blueglacier.email.Email.fillEmailContents(Email.java:71) \~\[email-mime-parser-1.0.5.jar:na\]
at tech.blueglacier.parser.CustomContentHandler.body(CustomContentHandler.java:36) \~\[email-mime-parser-1.0.5.jar:na\]
at org.apache.james.mime4j.parser.MimeStreamParser.parse(MimeStreamParser.java:133) \~\[apache-mime4j-core-0.8.9.jar:0.8.9\]
at dev.fetchmail.koala.services.ImapMailReceiverImpl.fetchMail(ImapMailReceiverImpl.java:81) \~\[classes/:na\]
at dev.fetchmail.koala.KoalaApplication.run(KoalaApplication.java:21) \~\[classes/:na\]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:769) \~\[spring-boot-3.0.4.jar:3.0.4\]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:753) \~\[spring-boot-3.0.4.jar:3.0.4\]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:317) \~\[spring-boot-3.0.4.jar:3.0.4\]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1304) \~\[spring-boot-3.0.4.jar:3.0.4\]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1293) \~\[spring-boot-3.0.4.jar:3.0.4\]