fix(knowledge):Fix KB document questions list check logic

[vnicers]

Description

When editing the name of a KB document, if there are no question and answer pairs by default, the frontend will not pass the questions field, and the questions on the backend are None instead of empty list

How Has This Been Tested?

Snapshots:

Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[Aries-ckt]

LGTM, thanks for your contribution.

[fangyinc]

LGTM