Skip storing the dispatcher target when the servlet context returns no dispatcher (quick fix)

[dougqh]

What Does This Do

ServletContextInstrumentation.RequestDispatcherTargetAdvice now returns early when getRequestDispatcher / getNamedDispatcher returns null, instead of using the null dispatcher as a context-store key.

Motivation

Error Tracking: https://app.datadoghq.com/error-tracking/issue/7ddef69a-aab1-11f0-8060-da7ad0900002 ("Failed to handle exception in instrumentation for org.apache.catalina.core.ApplicationContext"):

java.lang.NullPointerException
  at datadog.trace.agent.tooling.WeakMaps$Adapter.put(WeakMaps.java:75)
  at datadog.trace.bootstrap.WeakMapContextStore.put(WeakMapContextStore.java:31)
  at ... (advice on org.apache.catalina.core.ApplicationContext)

Servlet containers return null for an unknown path or servlet name. Tomcat's ApplicationContext does this, for example. A null key fails the KeyWithValue check in FieldBackedContextStore, so it falls through to the weak-map fallback, and WeakConcurrentMap rejects null keys. The error was suppressed and logged, so it didn't break the app, but it showed up as noise in instrumentation telemetry.

This is the put-side companion of #12692, which fixed the get side (a null servlet context key in the IAST getSession advice).

Additional Notes

• New JUnit 5 test ServletContextNullDispatcherTest (javax-servlet-common). It uses a ServletContext that returns null dispatchers. Before the fix it fails through AbstractInstrumentationTest's instrumentation-error check, with the same WeakMaps$Adapter.put(WeakMaps.java:75) NPE stack as production. After the fix it passes.
• :dd-java-agent:instrumentation:servlet:javax-servlet:javax-servlet-common:test, spotlessCheck and spotbugsMain pass.
• There is no jakarta counterpart of this advice, so no other call site needs the change.

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More details

The null guard prevents missing dispatchers from reaching the context store while preserving target storage for non-null dispatchers. Regression coverage addresses both dispatcher lookup methods.

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[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	14.62 s	14.64 s	[-0.9%; +0.6%] (no difference)
startup:insecure-bank:tracing:Agent	13.56 s	13.53 s	[-0.5%; +1.0%] (no difference)
startup:petclinic:appsec:Agent	17.65 s	17.48 s	[+0.2%; +1.8%] (maybe worse)
startup:petclinic:iast:Agent	17.30 s	17.45 s	[-1.7%; +0.0%] (no difference)
startup:petclinic:profiling:Agent	17.32 s	16.59 s	[+0.2%; +8.5%] (maybe worse)
startup:petclinic:sca:Agent	17.63 s	17.56 s	[-0.6%; +1.3%] (no difference)
startup:petclinic:tracing:Agent	16.50 s	16.21 s	[-2.5%; +6.2%] (no difference)

Commit: 6858d091 · CI Pipeline · Benchmarking Platform UI

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Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[dd-octo-sts]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-10-09 19:06:53 UTC ℹ️ Start processing command /merge

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2026-10-09 19:06:57 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in master is approximately 1h (p90).

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2026-10-09 20:00:58 UTC ❌ MergeQueue: The build pipeline contains failing jobs for this merge request

Build pipeline has failing jobs for 4fc605b:

• test_ssi_smoke: [ibm8, 1/8]

⚠️ Do NOT retry failed jobs directly (why?).

What to do next?

• Investigate the failures and when ready, re-add your pull request to the queue!
• If your PR checks are green, try to rebase/merge. It might be because the CI run is a bit old.
• Any question, go check the FAQ.

Details

Since those jobs are not marked as being allowed to fail, the pipeline will most likely fail.
Therefore, and to allow other builds to be processed, this merge request has been rejected and the pipeline got canceled.

[dd-octo-sts]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-10-09 20:20:53 UTC ℹ️ Start processing command /merge

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2026-10-09 20:20:58 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in master is approximately 1h (p90).

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2026-10-09 22:07:30 UTC ℹ️ MergeQueue: This merge request was merged