*: add non-nil check to avoid panic

[crazycs520]

Signed-off-by: crazycs520 crazycs520@gmail.com

What problem does this PR solve?

Issue Number: close #30252

What is changed and how it works?

• Add non-nil check.

In fact, I didn’t understand why the StatementContext.digestMemo.digest value is nil. I check all related function call chain, normally, it should never happen. So I just add some non-nil check to avoid panic.

Check List

Tests

• No code

Side effects

• N/A

Documentation

• N/A

Release note

None

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[crazycs520]

@tangenta @wjhuang2016 PTAL

[tangenta]

@crazycs520 I don't think this is a good way to fix it, because it can cause another nil-pointer problem.

We need to find out the root cause. How about adding a warning log in InitSQLDigest and printing the stack?

[crazycs520]

@crazycs520 I don't think this is a good way to fix it, because it can cause another nil-pointer problem.

We need to find out the root cause. How about adding a warning log in InitSQLDigest and printing the stack?

Anyhow, this PR can avoid the risk of potential panic, and does not affect the correctness.

I am not sure about adding log to print the stack to troubleshoot the issue.

[tangenta]

@crazycs520 I mean we should prevent StatementContext.digestMemo.digest to be nil, so that we don't need to add not-nil check to every usage.