[BugFix] Check optional params before .get() call in gqa_rope_write_cache

[K11OntheBoat]

Motivation

在gqa_rope_write_cache中, 存在针对 为空的optional tensor 使用.get()方法的情况；导致Paddle框架Assert错误:
python: paddle/include/paddle/utils/optional.h:563: paddle::optional::reference_const_type paddle::optional::get() const [with T = paddle::Tensor; reference_const_type = const paddle::Tensor&]: Assertion `this->is_initialized()' failed.”

Modifications

此PR采用更标准的C++写法，用指针表示可选参数, 不存在的Optional不使用 .get()方法，参数用nullptr向下传入的方法，可以修复此Assertion报错.

Note:

K11OntheBoat@2eea6fa 此PR給dev和2.6提了，规避了本PR处理的bug，但是那个PR并没提给2.5； 所以本PR专給2.5修复Bug使用

[paddle-bot]

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✅ Jiang-Jia-Jun
❌ K11OntheBoat

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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[PaddlePaddle-bot]

🤖 AI Code Review | 2026-04-13

📋 Review 摘要

PR 概述：修复 gqa_rope_write_cache 中 optional tensor 为空时调用 .get() 导致的断言错误，将参数从引用改为指针方式处理。

变更范围：custom_ops/gpu_ops/append_attn/

影响面 Tag：[BugFix] [OP]

📝 PR 规范检查

✅ PR 标题包含有效的 [BugFix] 标签
✅ PR 描述完整，包含 Motivation 和 Modifications

问题

级别	文件	概述
🔴 Bug	custom_ops/gpu_ops/append_attn/gqa_rope_write_cache.cu:1240	cache_int8/fp8 分支缺少空指针检查
🔴 Bug	custom_ops/gpu_ops/append_attn/gqa_rope_write_cache.cu:1276	cache_int4_zp 分支缺少空指针检查

总体评价

PR 的修复方向正确，将参数类型改为指针允许传递 nullptr。但 AppendCacheKV 函数内部在解引用指针前缺少防御性检查，如果 cache_quant_type 需要某参数但传入的是 nullptr，会导致空指针解引用崩溃而非清晰的错误提示。建议添加断言或参数有效性检查。

[zoooo0820]

LGTM