Error: Could not find the 'robot' element in the xml file

[Zhehui-Huang]

When I transfer sdf model to usd model. I met the issue below. Error: Could not find the 'robot' element in the xml file at line 109 in /build/urdfdom-VnCcob/urdfdom-1.0.4+ds/urdf_parser/src/model.cpp Errors encountered: Error Code 1: Msg: Unable to read file:model.sdf

Here is the sdf file: https://github.com/bitcraze/crazyflie-simulation/blob/main/gazebo-ignition/crazyflie/model.sdf