BanyanDB mixed the empty value and null value of a str type. @hanahmily

[wu-sheng]

This is a bug introduced by the BanyanDB server-side. It mixed the empty value and null value of a str type. @hanahmily

Originally posted by @wu-sheng in #13617 (comment)

Thread https://the-asf.slack.com/archives/CHQ1L4T54/p1765777235936089

cc @xiongxoy