TestSyncLoadOnObjectWhichCanNotFoundInStorage errors like nil pointer dereference

[AilinKid]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftidb%2Fghpr_unit_test/detail/ghpr_unit_test/24158/tests

2. What did you expect to see? (Required)

TestSyncLoadOnObjectWhichCanNotFoundInStorage test sucessfully

3. What did you see instead (Required)

--- FAIL: TestSyncLoadOnObjectWhichCanNotFoundInStorage (51.04s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x8679bb8]
goroutine 49 [running]:
testing.tRunner.func1.2({0x8d2e500, 0xd0e4620})
	GOROOT/src/testing/testing.go:1632 +0x3fc
testing.tRunner.func1()
	GOROOT/src/testing/testing.go:1635 +0x6b6
panic({0x8d2e500?, 0xd0e4620?})
	GOROOT/src/runtime/panic.go:785 +0x132
pkg/statistics/handle/syncload/syncload_test_test.TestSyncLoadOnObjectWhichCanNotFoundInStorage(0xc00120d520)
	pkg/statistics/handle/syncload/stats_syncload_test.go:469 +0x12d8
testing.tRunner(0xc00120d520, 0x96df748)
	GOROOT/src/testing/testing.go:1690 +0x227
created by testing.(*T).Run in goroutine 1
	GOROOT/src/testing/testing.go:1743 +0x826

4. What is your TiDB version? (Required)

master

[AilinKid]

/cc @hawkingrei @winoros