Fix NullPointerException in Exception Replay

[jpbempel]

What Does This Do

For FastThrow, getStackTrace can return null instead of empty StackTraceElement array

Motivation

Additional Notes

Contributor Checklist

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Jira ticket: DEBUG-6173

[dd-octo-sts]

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[datadog-prod-us1-6]

The new null check calls getStackTrace() twice for each exception with a non-empty stack. The second call copies the stack array again before the circuit breaker can reject the exception.

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[pr-commenter]

Debugger benchmarks

Parameters

	Baseline	Candidate
baseline_or_candidate	baseline	candidate
ci_job_date	1789019692	1789020019
end_time	2026-09-10T05:56:22	2026-09-10T06:01:49
git_branch	master	jpbempel/fix-npe-getStackTrace
git_commit_sha	a4b447e	027c1bf
start_time	2026-09-10T05:54:53	2026-09-10T06:00:20

See matching parameters

	Baseline	Candidate
ci_job_id	2030681168	2030681168
ci_pipeline_id	136529958	136529958
cpu_model	Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz	Intel(R) Xeon(R) Platinum 8175M CPU @ 2.50GHz
git_commit_date	1789019009	1789019009

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 10 metrics, 5 unstable metrics.

See unchanged results

scenario	Δ mean agg_http_req_duration_min	Δ mean agg_http_req_duration_p50	Δ mean agg_http_req_duration_p75	Δ mean agg_http_req_duration_p99	Δ mean throughput
scenario:noprobe	unstable [-21.645µs; +13.039µs] or [-6.540%; +3.940%]	unstable [-33.666µs; +25.245µs] or [-9.302%; +6.975%]	unstable [-41.698µs; +34.423µs] or [-11.109%; +9.171%]	unstable [+1.326µs; +177.458µs] or [+0.113%; +15.117%]	same
scenario:basic	same	same	same	unstable [+13.500µs; +218.278µs] or [+1.353%; +21.871%]	same
scenario:loop	same	same	same	same	same

Request duration reports for reports

gantt
    title reports - request duration [CI 0.99] : candidate=None, baseline=None
    dateFormat X
    axisFormat %s
section baseline
noprobe (361.927 µs) : 333, 391
.   : milestone, 362,
basic (341.859 µs) : 335, 349
.   : milestone, 342,
loop (8.116 ms) : 8051, 8180
.   : milestone, 8116,
section candidate
noprobe (357.716 µs) : 330, 385
.   : milestone, 358,
basic (338.694 µs) : 332, 346
.   : milestone, 339,
loop (8.116 ms) : 8052, 8181
.   : milestone, 8116,

Loading

• baseline results

Scenario	Request median duration [CI 0.99]
noprobe	361.927 µs [333.31 µs, 390.545 µs]
basic	341.859 µs [334.961 µs, 348.757 µs]
loop	8.116 ms [8.051 ms, 8.18 ms]

• candidate results

Scenario	Request median duration [CI 0.99]
noprobe	357.716 µs [330.405 µs, 385.028 µs]
basic	338.694 µs [331.77 µs, 345.619 µs]
loop	8.116 ms [8.052 ms, 8.181 ms]

[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	14.90 s	14.66 s	[+0.7%; +2.6%] (maybe worse)
startup:insecure-bank:tracing:Agent	13.68 s	13.73 s	[-1.3%; +0.6%] (no difference)
startup:petclinic:appsec:Agent	17.56 s	17.48 s	[-0.3%; +1.3%] (no difference)
startup:petclinic:iast:Agent	17.43 s	16.84 s	[-0.7%; +7.7%] (no difference)
startup:petclinic:profiling:Agent	17.36 s	17.41 s	[-1.3%; +0.7%] (no difference)
startup:petclinic:sca:Agent	17.59 s	16.87 s	[-0.1%; +8.7%] (no difference)
startup:petclinic:tracing:Agent	16.55 s	16.62 s	[-1.3%; +0.5%] (no difference)

Commit: 027c1bfa · CI Pipeline · Benchmarking Platform UI

---

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

[datadog-prod-us1-6]

More details

The null check prevents Exception Replay from reading the length of a null stack trace. The existing empty-stack behavior and circuit-breaker path stay unchanged.

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[dd-octo-sts]

/merge

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2026-09-10 06:31:08 UTC ℹ️ Start processing command /merge

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2026-09-10 06:31:14 UTC ℹ️ MergeQueue: pull request added to the queue

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

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2026-09-10 07:25:15 UTC ℹ️ MergeQueue: This merge request was merged