Detecting collision with a static object using contact sensor

Hi, I am using ROS kinetic 1.12.13 and gazebo 7.13.0 I have a staic object in a gazebo world. This static object has camera, depth and contact sensors attached to it. I will refer to this object as "sensor_agent". When this sensor_agent collides with other non-static objects, the contact sensor outputs contact states but however I have a whole bunch of models in my world like building and trees which are static objects ( true ). When the sensor_agent collides with these static objects the, the contact states is empty. [Here](https://drive.google.com/open?id=1Ny8AypLAHQyG6E5Fham2g4XsPJUyHUjU) is sdf file of one of those static models. Is there any way I can detect collision with these static objects using contact sensor ? If not, is there any other way I can detect collision with these objects ? Thanks