In this diff, we are removing the database item internal check for the device's notification token filed.
We are fixing the bug where the database error occurs in the case when the device token in the database became empty and the server will return a database error when retrieving the token in the next client connection.
The field can be empty and the database check shouldn't fail on this. For more context please refer to the D5536.
Linear task: [[ https://linear.app/comm/issue/ENG-2060/implement-tunnelbroker-grpc-messagesstream-api-handler-in-rust | ENG-2060 ]]