openzipkin/zipkin · warning · NullPointerException

logger == null

Error message

logger == null

What it means

Defensive re-check in Collector's package-private constructor: the builder's logger must not be null. In practice unreachable through Collector.newBuilder(Class) because that entry point creates the logger from a non-null class; the guard protects against future/alternate construction paths and bugs in the builder itself.

Source

Thrown at zipkin-collector/core/src/main/java/zipkin2/collector/Collector.java:89

    /** Sets {@link {@link CollectorComponent.Builder#sampler(CollectorSampler)}} */
    public Builder sampler(CollectorSampler sampler) {
      if (sampler == null) throw new NullPointerException("sampler == null");
      this.sampler = sampler;
      return this;
    }

    public Collector build() {
      return new Collector(this);
    }
  }

  final Logger logger;
  final CollectorMetrics metrics;
  final CollectorSampler sampler;
  final StorageComponent storage;

  Collector(Builder builder) {
    if (builder.logger == null) throw new NullPointerException("logger == null");
    this.logger = builder.logger;
    this.metrics = builder.metrics == null ? CollectorMetrics.NOOP_METRICS : builder.metrics;
    if (builder.storage == null) throw new NullPointerException("storage == null");
    this.storage = builder.storage;
    this.sampler = builder.sampler == null ? CollectorSampler.ALWAYS_SAMPLE : builder.sampler;
  }

  public void accept(List<Span> spans, Callback<Void> callback) {
    accept(spans, callback, Runnable::run);
  }

  /**
   * Calls to get the storage component could be blocking. This ensures requests that block
   * callers (such as http or gRPC) do not add additional load during such events.
   *
   * @param executor the executor used to enqueue the storage request.
   */
  public void accept(List<Span> spans, Callback<Void> callback, Executor executor) {

View on GitHub (pinned to 878ce2a1fa)

Solutions

1. Use the public entry point Collector.newBuilder(YourCollectorClass.class) which always sets a logger.
2. If you forked the builder, ensure the logger field is final and set in the constructor.

When it happens

Trigger: Constructing Collector via a Builder obtained only through Collector.newBuilder(...) after nulling the logger reflectively, or a new entry point that skips logger initialization. Not reachable from normal public API use.

Common situations: Reflection/mocking frameworks (e.g. Mockito constructing with null fields); modified or forked builder code that loses the logger assignment.

Related errors

• loggingClass == null
• metrics == null
• storage == null
• metrics == null
• sampler == null

AI-assisted analysis of openzipkin/zipkin@878ce2a1fa (2026-08-14). Data as JSON: /api/errors/0e05e7eccb647a35. Report an issue: GitHub.