return empty and print error
when using <include> with <name> use modelname@something instead of a different name to keep gazebo2rviz working
rosrun tf2_ros static_transform_publisher 0 0 0  0 0 0 1 PARENT CHILD    not the other way round
works as required, BUT should refactor everything SDF/URDF related using the classes from sdf2urdf ... one of these days
again this should be based an a clean common set of classes for sdf ... but hack works for now
fix, add ignore capability ... for reminder during rewrite