Can Azir Sovereign bring his token units to an empty battlefield as there are no defenders in an empty battlefield?

Yes, Azir, Sovereign can move his token units to an empty battlefield when he attacks.

According to the RiftJudge FAQ (ID 2127), when Azir attacks, his ability triggers and allows you to move any number of your token units to "this battlefield" (the battlefield where Azir is currently attacking).

There are no restrictions preventing you from moving tokens to an empty battlefield. The only requirement is that Azir must be at a valid battlefield for the ability to resolve. If he is at an empty battlefield, that is a valid location, and the tokens will move there successfully.

As noted in the FAQ:

• "This battlefield" is defined relative to Azir's current location.
• If Azir is at an empty battlefield, the tokens move to that battlefield.
• If Azir were removed or moved to base before the trigger resolved, the ability would whiff because "this battlefield" would no longer be a valid location.