PatchPilot fix for #1 - #2

Fixes #1

PatchPilot task

• Task: 7618be68-7593-4f1b-9e06-bc4e117f63ef
• Triggered by: bingqin2
• Branch: patchpilot/7618be68-7593-4f1b-9e06-bc4e117f63ef
• Language: java
• Build system: maven
• Verification: mvn test
• Detection reason: Detected Maven project

Verification and review

• Verification result: mvn test exited 0 in 11547 ms.
• Patch review:
• Patch review decision: APPROVE
• Patch review reason: The edit adds the exact guard clause throwing IllegalArgumentException with the required message and leaves other methods unchanged, fulfilling the issue and fix plan.
• Patch review confidence: HIGH
• Patch review follow-up: Run CalculatorTest#should_reject_division_by_zero_with_a_clear_message to confirm it passes.
• Patch review edited files: src/main/java/demo/Calculator.java
• Patch reviewed at: 2026-09-04T01:35:03.568707Z
• PatchPilot opened this PR only after every recorded adapter verification passed.
• Verification commands are selected by the detected repository adapter, not by arbitrary issue text.
• PatchPilot does not auto-merge Pull Requests.