apache/maven · error · XMLStreamException

Missing required value for attribute '{}'

Error message

Missing required value for attribute '{}'

What it means

Thrown by the Modello-generated StAX reader (template src/mdo/reader.vm) from getRequiredAttributeValue when an element declares a required attribute that is absent (attribute value is null). In strict mode this aborts parsing with javax.xml.stream.XMLStreamException; non-strict mode returns null for the attribute and parsing continues, which may surface later as an NPE or validation error downstream.

Source

Thrown at src/mdo/reader.vm:998

        return 0;
    } //-- long getLongValue(String, String, XMLStreamReader, boolean)

    /**
     * Method getRequiredAttributeValue.
     *
     * @param s a s object.
     * @param strict a strict object.
     * @param parser a parser object.
     * @param attribute a attribute object.
     * @throws XMLStreamException XMLStreamException if
     * any.
     * @return String
     */
    private String getRequiredAttributeValue(String s, String attribute, XMLStreamReader parser, boolean strict)
            throws XMLStreamException {
        if (s == null) {
            if (strict) {
                throw new XMLStreamException("Missing required value for attribute '" + attribute + "'", parser.getLocation(), null);
            }
        }
        return s;
    } //-- String getRequiredAttributeValue(String, String, XMLStreamReader, boolean)

    /**
     * Method getShortValue.
     *
     * @param s a s object.
     * @param strict a strict object.
     * @param parser a parser object.
     * @param attribute a attribute object.
     * @throws XMLStreamException XMLStreamException if
     * any.
     * @return short
     */
    private short getShortValue(String s, String attribute, XMLStreamReader parser, boolean strict)
            throws XMLStreamException {

View on GitHub (pinned to e4093d4e12)

Solutions

  1. Compare the element against the model schema/xdoc and add the missing required attribute with a valid value.
  2. Upgrade the producer (plugin/tool) that writes the file to a version matching the model the reader enforces.
  3. Regenerate the document from its source instead of hand-editing.
  4. If optional semantics are wanted, read with strict=false, then apply your own defaults for null attributes.

Example fix

<!-- before -->
<ruleset>
  <requireJavaVersion/>
</ruleset>
<!-- after (attribute now required by model) -->
<requireJavaVersion version="[17,)"/>
Defensive patterns

Strategy: validation

Validate before calling

// before parse: schema-validate so required attributes are checked up front
SchemaFactory f = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Validator v = f.newSchema(new StreamSource(modelXsd)).newValidator();
v.setErrorHandler(failFastHandler);
v.validate(new StreamSource(xmlFile));

Try / catch

try {
    reader.read(in, true);
} catch (XMLStreamException e) {
    if (e.getMessage().startsWith("Missing required value")) { /* report authoring error */ }
}

Prevention

When it happens

Trigger: Reading a model XML document in strict mode where an element carrying required attributes (per the mdo model, e.g. activationFile/property names, repository ids in some model versions) omits one, such as <file missing='the required one'/> or <activeByDefault/> without its id attribute.

Common situations: Documents written by older model versions that did not require the attribute; hand-authored XML missing mandatory attributes; elements refactored to add a new required attribute without regenerating the XML; whitespace-stripped attributes reduced to empty strings.

Related errors

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/848de2fbf982dc30. Report an issue: GitHub.