CI: TestFSOps error: can not set nil value

[zhoucheng361]

What happened:
https://github.com/juicedata/juicefs/actions/runs/13404731430/job/37442515893

go test ./pkg/meta/... -rapid.meta=tikv://127.0.0.1:2379/test -rapid.seed=13256 -rapid.checks=100000 -rapid.steps=200 -run "TestFSOps" -v -failfast -count=1 -timeout=30m -cover -coverpkg=./pkg/... -args -test.gocoverdir="/home/runner/work/juicefs/juicefs/cover"
	github.com/juicedata/juicefs/pkg/meta/pb		coverage: 0.0% of statements
=== RUN   TestFSOps
2025/02/19 03:21:45.669592 juicefs[3908] <ERROR>: error: can not set nil value
goroutine 12 [running]:
runtime/debug.Stack()
	/opt/hostedtoolcache/go/1.23.6/x64/src/runtime/debug/stack.go:26 +0x5e
github.com/juicedata/juicefs/pkg/meta.errno({0x1c7d4c0, 0x29106a0})
	/home/runner/work/juicefs/juicefs/pkg/meta/utils.go:125 +0xfc
github.com/juicedata/juicefs/pkg/meta.(*kvMeta).doSetXattr(0xc001351620, {0x1c9ed38, 0xc00189dc80}, 0x30?, {0xc0009bb380, 0x16}, {0xc0017ebbc6, 0x0, 0x5}, 0x0)
	/home/runner/work/juicefs/juicefs/pkg/meta/tkv.go:2661 +0x23b
github.com/juicedata/juicefs/pkg/meta.(*baseMeta).SetXattr(0xc000ad9908, {0x1c9ed38, 0xc00189dc80}, 0x3, {0xc0009bb380, 0x16}, {0xc0017ebbc6, 0x0, 0x5}, 0x0)
	/home/runner/work/juicefs/juicefs/pkg/meta/base.go:1833 +0x216
github.com/juicedata/juicefs/pkg/meta.(*fsMachine).SetXAttr(0xc001363470, 0xc000c30880)
	/home/runner/work/juicefs/juicefs/pkg/meta/random_test.go:1391 +0x22b
pgregory.net/rapid.runAction(0xc000c30880, 0xc0013634a0?)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/statemachine.go:174 +0x88
pgregory.net/rapid.(*stateMachine).executeAction(0xc001363500, 0xc000c30880)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/statemachine.go:149 +0xc9
pgregory.net/rapid.Run[...].func1()
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/statemachine.go:83 +0x[11](https://github.com/juicedata/juicefs/actions/runs/13404731430/job/37442515893#step:6:12)3
pgregory.net/rapid.checkOnce(0xc000c30880, 0xc0000dfa00?)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/engine.go:319 +0x8c
pgregory.net/rapid.findBug({0x1ca11b0, 0xc0000dfa00}, 0x186a0, 0x33c8, 0xc000c2bb60)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/engine.go:291 +0x23f
pgregory.net/rapid.doCheck({0x1ca11b0, 0xc0000dfa00}, {0x0, 0x0}, 0x186a0, 0x33c8, 0xc000c2bb60)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/engine.go:221 +0x105
pgregory.net/rapid.checkTB({0x1ca11b0, 0xc0000dfa00}, 0xc000c2bb60)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/engine.go:166 +0xec
pgregory.net/rapid.Check(0xc0000dfa00, 0xc000c2bb60)
	/home/runner/go/pkg/mod/pgregory.net/[email protected]/engine.go:93 +0x35
github.com/juicedata/juicefs/pkg/meta.TestFSOps(0xc0000dfa00)
	/home/runner/work/juicefs/juicefs/pkg/meta/random_test.go:2159 +0x11d
testing.tRunner(0xc0000dfa00, 0x1ac8a90)
	/opt/hostedtoolcache/go/1.23.6/x64/src/testing/testing.go:1690 +0xf4
created by testing.(*T).Run in goroutine 1
	/opt/hostedtoolcache/go/1.23.6/x64/src/testing/testing.go:1743 +0x390 [[email protected]:[12](https://github.com/juicedata/juicefs/actions/runs/13404731430/job/37442515893#step:6:13)5]
2025/02/19 03:21:45.763754 juicefs[3908] <ERROR>: error: can not set nil value
goroutine 12 [running]:

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?

Environment:

• JuiceFS version (use juicefs --version) or Hadoop Java SDK version:
• Cloud provider or hardware configuration running JuiceFS:
• OS (e.g cat /etc/os-release):
• Kernel (e.g. uname -a):
• Object storage (cloud provider and region, or self maintained):
• Metadata engine info (version, cloud provider managed or self maintained):
• Network connectivity (JuiceFS to metadata engine, JuiceFS to object storage):
• Others:

[davies]

Is the empty value useful? If not, we can return EINVAL for empty value.

[jiefenghuang]

not sure if there is a use case for this, like simply making a mark.