quarkusio/quarkus · error · IllegalArgumentException

Param was null

Error message

Param was null

What it means

ObjectToStringDelegate is a fallback HeaderDelegate for header types with no dedicated delegate; it serializes via Objects.toString. Its fromString always throws: first a null check ('Param was null'), then unconditionally, because generic object headers cannot be deserialized back from a string. This error means you passed null to a delegate that cannot parse anyway.

Source

Thrown at independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/headers/ObjectToStringDelegate.java:13

package org.jboss.resteasy.reactive.common.headers;

import java.util.Objects;

import jakarta.ws.rs.ext.RuntimeDelegate;

public class ObjectToStringDelegate implements RuntimeDelegate.HeaderDelegate<Object> {
    public static final ObjectToStringDelegate INSTANCE = new ObjectToStringDelegate();

    @Override
    public Object fromString(String value) {
        if (value == null)
            throw new IllegalArgumentException("Param was null");
        throw new IllegalArgumentException("Does not support fromString");
    }

    @Override
    public String toString(Object value) {
        if (value == null)
            throw new IllegalArgumentException("Param was null");
        return Objects.toString(value);
    }
}

View on GitHub (pinned to e1c734241f)

Solutions

1. Register a proper HeaderDelegate for the header's type via RuntimeDelegate.getInstance().createHeaderDelegate or a RuntimeDelegateDecorator so fromString is supported.
2. Parse the header manually with a known delegate (e.g. StringHeaderDelegate) if the type is truly String-like.
3. Null-check before invoking; note that even non-null input will throw 'Does not support fromString' here.

Example fix

// before
Object v = RuntimeDelegate.getInstance().createHeaderDelegate(MyHeader.class).fromString(raw);
// after
if (raw == null) { return null; }
MyHeader v = MyHeader.parse(raw); // or register a real HeaderDelegate for MyHeader

if (rawHeader == null) {
    return null; // nothing to parse
}

static <T> boolean hasRegisteredFromDelegate(Class<T> headerType) {
    try {
        RuntimeDelegate.getInstance().createHeaderDelegate(headerType);
        return true;
    } catch (IllegalArgumentException e) {
        return false;
    }
}

try {
    return delegate.fromString(raw);
} catch (IllegalArgumentException e) {
    throw new IllegalStateException("Header type has no parsing delegate: " + e.getMessage(), e);
}

When it happens

Trigger: Calling ObjectToStringDelegate.INSTANCE.fromString(null), or RuntimeDelegate header parsing routed to the fallback delegate with a null string for a header type lacking a registered fromString delegate.

Common situations: Using custom header value types not registered with RuntimeDelegate; server-side parsing of a request header whose type only supports toString; generic header-processing frameworks hitting the fallback path.

Related errors

• Media type was null
• param was null
• Does not support fromString
• Param was null
• param was null

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/9edaa82465428e4e. Report an issue: GitHub.