[hotfix-1097] 修复数据库字段为null时，同步空指针问题

[kinoxyz1]

Purpose of this pull request

Which issue you fix

Fixes #1097.

Checklist:

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[ll076110]

Could you try the val.isNullAt (int pos) method?

[kinoxyz1]

Could you try the val.isNullAt (int pos) method?

It has been modified.

[FlechazoW]

This is a useless imports.