quarkusio/quarkus · error · IllegalArgumentException

@${annotation} value cannot be blank. Offending method is: $

Error message

@${annotation} value cannot be blank. Offending method is: ${method}

What it means

Quarkus Reactive Messaging validates annotations like @Channel, @Connector or @Emitter on mediator methods: their value must be a non-empty string. During deployment, getValue reads the annotation instance's value; if it is absent, null, or empty it aborts the build with this IllegalArgumentException naming the offending method. It exists to fail fast instead of producing a mediator with an unusable/unnamed target.

Source

Thrown at extensions/smallrye-reactive-messaging/deployment/src/main/java/io/quarkus/smallrye/reactivemessaging/deployment/QuarkusMediatorConfigurationUtil.java:361

        }
        try {
            return Class.forName(className, false, cl);
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e);
        }
    }

    private static String getValue(MethodInfo methodInfo, DotName dotName) {
        AnnotationInstance annotationInstance = methodInfo.annotation(dotName);
        String value = null;

        if (annotationInstance != null) {
            if (annotationInstance.value() != null) {
                value = annotationInstance.value().asString();

            }
            if ((value == null) || value.isEmpty()) {
                throw new IllegalArgumentException(
                        "@" + dotName.withoutPackagePrefix() + " value cannot be blank. Offending method is: "
                                + fullMethodName(methodInfo));
            }

            // TODO: does it make sense to validate the name with the supplied configuration?
        }

        return value;
    }

    private static List<String> getValues(MethodInfo methodInfo, DotName dotName) {
        return methodInfo.annotations().stream().filter(ai -> ai.name().equals(dotName))
                .map(ai -> ai.value().asString())
                .collect(Collectors.toList());
    }

    private static List<String> getIncomingValues(MethodInfo methodInfo) {
        return methodInfo.annotations().stream().filter(ai -> ai.name().equals(INCOMINGS))

View on GitHub (pinned to e1c734241f)

Solutions

1. Give the annotation an explicit non-blank value, e.g. @Channel("prices").
2. If the channel name is configured externally, still supply the value (Quarkus can map it via configuration like mp.messaging.outgoing.<name>.connector).
3. Remove the annotation entirely if it is not needed.
4. Check the method named in the message for other empty-value annotations.

Example fix

// before
@Outgoing(""
)
Multi<String> emit() { ... }
// after
@Outgoing("my-channel")
Multi<String> emit() { ... }

fun validateChannelValue(annotation: Annotation?): Boolean =
    when (annotation) {
        is Channel -> annotation.value.isNotBlank()
        else -> true
    }
// Ensure every @Channel/@Connector/@Emitter has a non-blank value before build.

When it happens

Trigger: Annotating a method with @Channel/@Connector/@Emitter (or similar) with no value, e.g. @Channel or @Channel("") on an @Incoming/@Outgoing method.

Common situations: Refactoring away a literal string and leaving the annotation empty; generating code/templates with placeholder annotation values left blank; copying an annotation example that used a named parameter you removed.

Related errors

• Emitter configuration for channel `${channel}` is different
• @ExactlyOnce on method ${methodName} requires both @Incoming
• name cannot be null
• Either location or predicate must be set
• At least one package name must be specified

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/8a8afeddd0a28d00. Report an issue: GitHub.