What causes "type must not be null" in quarkusio/quarkus?

Pass the concrete class explicitly, e.g. content(dto, MyDto.class).

quarkusio/quarkus · error · IllegalArgumentException

type must not be null

Error message

type must not be null

What it means

EntityPart.Builder.content(T, Class<? extends T>) requires an explicit Class used to select the matching MessageBodyWriter; the type argument must not be null or IllegalArgumentException is thrown. The content object itself is validated first.

Source

Thrown at independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/jaxrs/EntityPartBuilderImpl.java:111

    @Override
    public EntityPart.Builder content(InputStream content) throws IllegalArgumentException {
        if (content == null) {
            throw new IllegalArgumentException("content must not be null");
        }
        this.content = content;
        this.contentType = null;
        this.contentGenericType = null;
        return this;
    }

    @Override
    public <T> EntityPart.Builder content(T content, Class<? extends T> type) throws IllegalArgumentException {
        if (content == null) {
            throw new IllegalArgumentException("content must not be null");
        }
        if (type == null) {
            throw new IllegalArgumentException("type must not be null");
        }
        this.content = content;
        this.contentType = type;
        this.contentGenericType = type;
        return this;
    }

    @Override
    public <T> EntityPart.Builder content(T content, GenericType<T> type) throws IllegalArgumentException {
        if (content == null) {
            throw new IllegalArgumentException("content must not be null");
        }
        if (type == null) {
            throw new IllegalArgumentException("type must not be null");
        }
        this.content = content;
        this.contentType = type.getRawType();
        this.contentGenericType = type.getType();

View on GitHub (pinned to e1c734241f)

Solutions

Pass the concrete class explicitly, e.g. content(dto, MyDto.class).
Derive the class safely from the entity: entity.getClass() (valid since entity must be non-null anyway).
In generic helpers, capture the Class as a method parameter and validate it.
Fix the caller that passes a null Class variable.

Example fix

// before
builder.content(entity, typeClass); // typeClass may be null

// after
builder.content(entity, entity.getClass());

Defensive patterns

Strategy: validation

Validate before calling

Objects.requireNonNull(type, "content type must not be null");
builder.content(entity, type);

Type guard

<T> Class<? extends T> typeOf(T entity) {
    @SuppressWarnings("unchecked")
    Class<? extends T> c = (Class<? extends T>) entity.getClass();
    return c;
}

Try / catch

try {
    builder.content(entity, type);
} catch (IllegalArgumentException e) {
    builder.content(entity, entity.getClass());
}

Prevention

Always pass an explicit class literal (MyDto.class) to content(T, Class).
In generic helpers, take the Class as a parameter rather than inferring it.
Use entity.getClass() when no explicit type is available.

When it happens

Trigger: Calling partBuilder.content(entity, null) — passing the entity without a concrete Class, e.g. when the type is derived from a nullable variable or generics erasure.

Common situations: Generic helper methods that capture the type from a parameter which is null; using getClass() on a null entity or forwarding an uninitialized Class variable; reflection-based builders.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/3a7cbe67df009696. Report an issue: GitHub.