apache/maven · error · ComponentConfigurationException

Basic element '{}' must not contain child elements

Error message

Basic element '{}' must not contain child elements

What it means

In the same composite-binding path, when the resolved value is not an instance of the set(...) parameter type, EnhancedCompositeBeanHelper falls back to converting the element's text via convertProperty - but only if the element has no child elements; a basic (scalar) element carrying nested XML is structurally invalid and throws ComponentConfigurationException "Basic element '<name>' must not contain child elements".

Source

Thrown at impl/maven-core/src/main/java/org/apache/maven/configuration/internal/EnhancedCompositeBeanHelper.java:98

        // Find the default "set" method
        MethodInfo setterInfo = findCachedMethod(beanType, "", null);
        if (setterInfo == null) {
            // Look for any method named "set" with one parameter
            Map<String, MethodInfo> classMethodCache = METHOD_CACHE.computeIfAbsent(beanType, this::buildMethodCache);
            setterInfo = classMethodCache.get("set");
        }

        if (setterInfo == null) {
            throw new ComponentConfigurationException(configuration, "Cannot find default setter in " + beanType);
        }

        Object value = defaultValue;
        TypeLiteral<?> paramType = TypeLiteral.get(setterInfo.parameterType);

        if (!paramType.getRawType().isInstance(value)) {
            if (configuration.getChildCount() > 0) {
                throw new ComponentConfigurationException(
                        "Basic element '" + configuration.getName() + "' must not contain child elements");
            }
            value = convertProperty(beanType, paramType.getRawType(), paramType.getType(), configuration);
        }

        if (value != null) {
            try {
                if (listener != null) {
                    listener.notifyFieldChangeUsingSetter("", value, bean);
                }
                setterInfo.method.invoke(bean, value);
            } catch (IllegalAccessException | InvocationTargetException | LinkageError e) {
                throw new ComponentConfigurationException(configuration, "Cannot set default", e);
            }
        }
    }

    /**

View on GitHub (pinned to e4093d4e12)

Solutions

1. Flatten the element: give it text content (`<threadCount>4</threadCount>`) instead of children.
2. Check the parameter's declared type for your plugin version and reshape the configuration to match.
3. Pin or upgrade to the plugin version whose configuration style the existing XML follows.

Example fix

<!-- before -->
<configuration>
  <threadCount><max>4</max></threadCount>
</configuration>

<!-- after -->
<configuration>
  <threadCount>4</threadCount>
</configuration>

try {
    configurator.configureBean(request);
} catch (BeanConfigurationException e) {
    if (e.getMessage() != null && e.getMessage().contains("must not contain child elements")) {
        reportNestedScalarParameter(e); // flatten <param><child>x</child></param> to <param>x</param>
    } else {
        throw e;
    }
}

When it happens

Trigger: Configuration like `<threadCount><max>4</max></threadCount>` where the target set(...) accepts a scalar (e.g. String or int): the child elements make text conversion impossible.

Common situations: Upgrading a plugin whose parameter changed from a composite type to a simple type while old configuration kept nested XML; copy-pasting configuration between parameters of different shapes; stale examples in docs.

Related errors

• Unable to convert configuration to xml node
• Cannot find default setter in {}
• Cannot read metadata from '{}': {}
• Cannot serialize project model for interpolation.
• Cannot read project model from interpolating filter of seria

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/52b613e36dac28d3. Report an issue: GitHub.