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

[yux0]

We see NPE in ReplayDecider with line: decisionTask.getHistory().getEvents().get(0).getWorkflowExecutionStartedEventAttributes();

In ReplayDecisionTaskHandler, we have special handling for sticky decision task that has a partial history. But we do not check the returned history. So add a check to get workflow history when sticky decision task

[gitar-bot]

⚠️ 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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[gitar-bot]

Code Review ⚠️ Changes requested 0 resolved / 1 findings

Adds a check for sticky decision tasks to prevent NPEs in ReplayDecider, but the implementation fails to guard against potential null values returned by getHistoryResponse.getHistory().

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

📄 src/main/java/com/uber/cadence/internal/replay/ReplayDecisionTaskHandler.java:277

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");
}

🤖 Prompt for agents

Code Review: Adds a check for sticky decision tasks to prevent NPEs in ReplayDecider, but the implementation fails to guard against potential null values returned by getHistoryResponse.getHistory().

1. ⚠️ Bug: Potential NPE on getHistoryResponse.getHistory() not guarded
   Files: src/main/java/com/uber/cadence/internal/replay/ReplayDecisionTaskHandler.java:277

   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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