Netflix/Hystrix · error · IllegalArgumentException

HystrixNetworkAuditorEventListener can not be NULL

Error message

HystrixNetworkAuditorEventListener can not be NULL

What it means

HystrixNetworkAuditorAgent is a javaagent that forwards socket/NIO activity to a registered HystrixNetworkAuditorEventListener (the 'bridge'). registerEventListener guards its single required argument with an explicit null check throwing IllegalArgumentException, because a null bridge would silently disable all network-event auditing.

Source

Thrown at hystrix-contrib/hystrix-network-auditor-agent/src/main/java/com/netflix/hystrix/contrib/networkauditor/HystrixNetworkAuditorAgent.java:54

        inst.addTransformer(new NetworkClassTransform());
    }

    /**
     * Invoked by instrumented code when network access occurs.
     */
    public static void notifyOfNetworkEvent() {
        bridge.handleNetworkEvent();
    }

    /**
     * Register the implementation of the {@link HystrixNetworkAuditorEventListener} that will receive the events.
     * 
     * @param bridge
     *            {@link HystrixNetworkAuditorEventListener} implementation
     */
    public static void registerEventListener(HystrixNetworkAuditorEventListener bridge) {
        if (bridge == null) {
            throw new IllegalArgumentException("HystrixNetworkAuditorEventListener can not be NULL");
        }
        HystrixNetworkAuditorAgent.bridge = bridge;
    }

}

View on GitHub (pinned to 5ce3bc58c3)

Solutions

1. Fix the construction path so the listener instance is non-null before registering (check the DI bean exists)
2. Register defensively only when the listener is available, failing fast with a clear boot error if the auditor is enabled without a listener
3. Pass a no-op implementation rather than null if auditing is optional in some profiles
4. Add a startup assertion/log immediately after registration

Example fix

// before
HystrixNetworkAuditorAgent.registerEventListener(listenerBean()); // may return null

// after
HystrixNetworkAuditorEventListener listener = listenerBean();
if (listener == null) throw new IllegalStateException("network auditor enabled but no listener configured");
HystrixNetworkAuditorAgent.registerEventListener(listener);

if (listener == null) {
    throw new IllegalStateException("Network auditor enabled but listener is null — check DI wiring");
}
HystrixNetworkAuditorAgent.registerEventListener(listener);

null // Java: use Objects.requireNonNull; no type-narrowing involved
Objects.requireNonNull(listener, "auditor listener");

catch (IllegalArgumentException e) { log.error("registerEventListener(null) — fix listener construction", e); failBoot(e); }

When it happens

Trigger: Calling HystrixNetworkAuditorAgent.registerEventListener(null) — typically from agent premain/application boot code that failed to construct the listener (e.g. dependency injection returned null, or a config-driven conditional listener that was never created).

Common situations: Wiring the auditor agent in a DI container where the listener bean is missing/conditional; test harnesses registering a no-op that evaluates to null; refactoring listener construction so the instance is created after registration is attempted.

Related errors

• Failed trying to wrap class: " + className
• Failed trying to wrap constructor of class: " + className
• Failed trying to wrap method [" + method.getName() + "] of c
• method cannot be annotated with HystrixCommand and HystrixCo
• Collapser method must have one argument: {}

AI-assisted analysis of Netflix/Hystrix@5ce3bc58c3 (2026-08-14). Data as JSON: /api/errors/e7b58c6a4e66ee4a. Report an issue: GitHub.