openzipkin/zipkin · error · NullPointerException

metrics == null

Error message

metrics == null

What it means

ActiveMQCollector.Builder.metrics is a required setter: passing null throws NullPointerException immediately (fail-fast contract used throughout Zipkin collectors). The metrics object is also scoped to the 'activemq' transport via CollectorMetrics.forTransport, so the collector can report messages/spans/bytes per transport.

Source

Thrown at zipkin-collector/activemq/src/main/java/zipkin2/collector/activemq/ActiveMQCollector.java:43

  public static final class Builder extends CollectorComponent.Builder {
    Collector.Builder delegate = Collector.newBuilder(ActiveMQCollector.class);
    CollectorMetrics metrics = CollectorMetrics.NOOP_METRICS;
    ActiveMQConnectionFactory connectionFactory;
    String queue = "zipkin";
    int concurrency = 1;

    @Override public Builder storage(StorageComponent storage) {
      this.delegate.storage(storage);
      return this;
    }

    @Override public Builder sampler(CollectorSampler sampler) {
      this.delegate.sampler(sampler);
      return this;
    }

    @Override public Builder metrics(CollectorMetrics metrics) {
      if (metrics == null) throw new NullPointerException("metrics == null");
      this.metrics = metrics.forTransport("activemq");
      this.delegate.metrics(this.metrics);
      return this;
    }

    public Builder connectionFactory(ActiveMQConnectionFactory connectionFactory) {
      if (connectionFactory == null) throw new NullPointerException("connectionFactory == null");
      this.connectionFactory = connectionFactory;
      return this;
    }

    /** Queue zipkin spans will be consumed from. Defaults to "zipkin". */
    public Builder queue(String queue) {
      if (queue == null) throw new NullPointerException("queue == null");
      this.queue = queue;
      return this;
    }

View on GitHub (pinned to 878ce2a1fa)

Solutions

1. Pass a real CollectorMetrics instance, at minimum CollectorMetrics.NOOP_METRICS if you don't want metrics.
2. Fix the dependency wiring so the metrics binding (e.g. InMemoryCollectorMetrics for tests) is provided.
3. If null came from a config lookup, default it: metrics != null ? metrics : CollectorMetrics.NOOP_METRICS.

Example fix

// before
builder.metrics(config.get("metrics")); // returns null -> NPE

// after
CollectorMetrics m = config.get("metrics");
builder.metrics(m != null ? m : CollectorMetrics.NOOP_METRICS);

java
if (metrics == null) metrics = CollectorMetrics.NOOP_METRICS;
builder.metrics(metrics);

When it happens

Trigger: Calling ActiveMQCollector.newBuilder().metrics(null) — typically when a wiring/framework config property for metrics is absent and the code forwards null unconditionally.

Common situations: DI/Guice/Spring wiring where the metrics binding is missing; copying an example that assumed an implicit default; test code that only sets storage and connectionFactory.

Related errors

• connectionFactory == null
• queue == null
• concurrency < 1
• storage == null
• metrics == null

AI-assisted analysis of openzipkin/zipkin@878ce2a1fa (2026-08-14). Data as JSON: /api/errors/9020fd6f923326a2. Report an issue: GitHub.