apache/maven · error · IllegalArgumentException

writer or outputStream must be non null

Error message

writer or outputStream must be non null

What it means

DefaultSettingsXmlFactory.write accepts only a Writer or an OutputStream - there is no path support on this factory. If both are null the call is rejected with IllegalArgumentException before serialization starts.

Solutions

1. Pass .writer(...) or .outputStream(...) on the request
2. To write a file, open it yourself: .outputStream(Files.newOutputStream(settingsPath)) inside try-with-resources
3. For in-memory output use .writer(new StringWriter())

Example fix

// before
settingsXmlFactory.write(XmlWriterRequest.builder()
    .content(settings)
    .path(settingsPath) // no path support on this factory
    .build()); // throws

// after
try (OutputStream os = Files.newOutputStream(settingsPath)) {
    settingsXmlFactory.write(XmlWriterRequest.builder()
        .content(settings)
        .outputStream(os)
        .build());
}

XmlWriterRequest<Settings> req = XmlWriterRequest.builder()
    .content(settings)
    .build();
if (req.getWriter() == null && req.getOutputStream() == null) {
    throw new IllegalStateException("settings write request has no writer or outputStream");
}
settingsXmlFactory.write(req);

When it happens

Trigger: Building a write request for Settings with only .path(...) set (ignored here), or with no output target at all.

Common situations: Porting write code from the model factory, which does support path targets; tests that set only the content.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• reader or inputStream must be non null
• writer or outputStream must be non null
• writer, outputStream or path must be non null
• writer, outputStream or path must be non null
• cannot be null

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/d800d2b3a4e3fc5b. Report an issue: GitHub.

Appendix: source

Thrown at impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultSettingsXmlFactory.java:81

            xml.setAddDefaultEntities(request.isAddDefaultEntities());
            if (reader != null) {
                return xml.read(reader, request.isStrict(), source);
            } else {
                return xml.read(inputStream, request.isStrict(), source);
            }
        } catch (Exception e) {
            throw new XmlReaderException("Unable to read settings: " + getMessage(e), getLocation(e), e);
        }
    }

    @Override
    public void write(XmlWriterRequest<Settings> request) throws XmlWriterException {
        nonNull(request, "request");
        Settings content = nonNull(request.getContent(), "content");
        OutputStream outputStream = request.getOutputStream();
        Writer writer = request.getWriter();
        if (writer == null && outputStream == null) {
            throw new IllegalArgumentException("writer or outputStream must be non null");
        }
        try {
            SettingsStaxWriter xmlWriter = new SettingsStaxWriter();
            xmlWriter.setAddLocationInformation(false);

            Function<Object, String> formatter = request.getInputLocationFormatter();
            if (formatter != null) {
                xmlWriter.setAddLocationInformation(true);
                Function<InputLocation, String> adapter = formatter::apply;
                xmlWriter.setStringFormatter(adapter);
            }

            if (writer != null) {
                xmlWriter.write(writer, content);
            } else {
                xmlWriter.write(outputStream, content);
            }
        } catch (Exception e) {

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