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fix(sticky): checking get workflow history when sticky decision task #631

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fix(sticky): checking get workflow history when sticky decision task #631

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3 changes: 3 additions & 0 deletions src/main/java/com/uber/cadence/internal/replay/ReplayDecisionTaskHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -274,6 +274,9 @@ private Decider createDecider(PollForDecisionTaskResponse decisionTask) throws E
.setExecution(decisionTask.getWorkflowExecution());
GetWorkflowExecutionHistoryResponse getHistoryResponse =
service.GetWorkflowExecutionHistory(getHistoryRequest);
if (getHistoryResponse.getHistory().getEventsSize() == 0) {
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@gitar-bot gitar-bot Bot May 1, 2026

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⚠️ Bug: Potential NPE on getHistoryResponse.getHistory() not guarded

The new check calls getHistoryResponse.getHistory().getEventsSize() but does not guard against getHistory() itself returning null. The original NPE described in the PR was on a similar chain (decisionTask.getHistory().getEvents().get(0)...). If the server returns a response with a null History field, this new code will throw an NPE instead of the intended RuntimeException.

Additionally, the same null risk exists on line 268 (decisionTask.getHistory().getEvents()) before the sticky check — if decisionTask.getHistory() is null, the method crashes before ever reaching the new guard. This is pre-existing, but worth noting since the PR aims to harden this path.

Suggested fix:

if (getHistoryResponse == null
    || getHistoryResponse.getHistory() == null
    || getHistoryResponse.getHistory().getEventsSize() == 0) {
  throw new RuntimeException("Failed to get workflow execution history for replay");
}

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throw new RuntimeException("Failed to get workflow execution history for replay");
}
decisionTask.setHistory(getHistoryResponse.getHistory());
decisionTask.setNextPageToken(getHistoryResponse.getNextPageToken());
}
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