quarkusio/quarkus · warning · IllegalArgumentException

type cannot be null

Error message

type cannot be null

What it means

RuntimeDelegateImpl.createHeaderDelegate requires a non-null Class argument per the JAX-RS RuntimeDelegate contract and throws IllegalArgumentException when type is null. Valid delegates exist for MediaType, Date, CacheControl, Cookie, EntityTag, Link, NewCookie, and URI types; unknown types later throw UnsupportedOperationException.

Source

Thrown at independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/jaxrs/RuntimeDelegateImpl.java:100

    public <T> RestResponse.ResponseBuilder<T> createRestResponseBuilder() {
        return factory.createRestResponse();
    }

    @Override
    public Variant.VariantListBuilder createVariantListBuilder() {
        return new VariantListBuilderImpl();
    }

    @Override
    public <T> T createEndpoint(Application application, Class<T> endpointType)
            throws IllegalArgumentException, UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }

    @Override
    public <T> HeaderDelegate<T> createHeaderDelegate(Class<T> type) throws IllegalArgumentException {
        if (type == null) {
            throw new IllegalArgumentException("type cannot be null");
        }
        if (type.equals(MediaType.class)) {
            return (HeaderDelegate<T>) MediaTypeHeaderDelegate.INSTANCE;
        } else if (Date.class.isAssignableFrom(type)) {
            // for Date, we do subtypes too, because ORM will instantiate java.util.Date as subtypes
            // and it's extremely likely we get those here, and we still have to generate a valid
            // date representation for them, rather than Object.toString which will be wrong
            return (HeaderDelegate<T>) DateDelegate.INSTANCE;
        } else if (type.equals(CacheControl.class)) {
            return (HeaderDelegate<T>) CacheControlDelegate.INSTANCE;
        } else if (type.equals(NewCookie.class)) {
            return (HeaderDelegate<T>) NewCookieHeaderDelegate.INSTANCE;
        } else if (type.equals(Cookie.class)) {
            return (HeaderDelegate<T>) CookieHeaderDelegate.INSTANCE;
        } else if (type.equals(EntityTag.class)) {
            return (HeaderDelegate<T>) EntityTagDelegate.INSTANCE;
        } else if (type.equals(Locale.class)) {
            return (HeaderDelegate<T>) LocaleDelegate.INSTANCE;

View on GitHub (pinned to e1c734241f)

Solutions

1. Ensure a concrete non-null Class is passed to createHeaderDelegate
2. If the type comes from generics/reflection, resolve the erased type before the call
3. Wrap in Objects.requireNonNull(type) early to fail fast with a clearer error
4. For unsupported types, register a custom HeaderDelegate or convert the value to String yourself

Example fix

// before
HeaderDelegate<Foo> d = rd.createHeaderDelegate(genericType); // genericType may be null
// after
if (genericType == null) {
    genericType = value.getClass();
}
HeaderDelegate<Foo> d = rd.createHeaderDelegate((Class<Foo>) genericType);

Objects.requireNonNull(type, "header delegate type must not be null");

boolean isDelegateSupported(Class<?> type) {
    return type != null && (MediaType.class.equals(type) || Date.class.isAssignableFrom(type)
        || CacheControl.class.equals(type) || Cookie.class.equals(type) || EntityTag.class.equals(type)
        || Link.class.equals(type) || NewCookie.class.equals(type) || URI.class.equals(type));
}

try {
    return rd.createHeaderDelegate(type);
} catch (IllegalArgumentException e) {
    return value -> value == null ? null : value.toString();
}

When it happens

Trigger: Calling createHeaderDelegate(null) directly, or indirectly through header serialization code that lost the type (reflection/generic erasure producing a null Class).

Common situations: Custom header-param converters resolving a runtime type that is null; framework integrations passing erased generic types; hand-written code building header delegates.

Related errors

• Param was null
• URI is null
• Scheme was null
• path is null
• Contextual parameter must not be null

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/aa5055ef0385514b. Report an issue: GitHub.