What does JointGroupPosition Controller do when it does not have pid gains set?

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Hello, Hello,

i am currently trying to simulate the UR3 Robot. Everything works but I am confused that there are no PID gains set in the "arm_controller_ur3.yaml" file:

 arm_controller:
  type: position_controllers/JointTrajectoryController
  joints:
     - shoulder_pan_joint
     - shoulder_lift_joint
     - elbow_joint
     - wrist_1_joint
     - wrist_2_joint
     - wrist_3_joint
  constraints:
      goal_time: 0.6
      stopped_velocity_tolerance: 0.05
      shoulder_pan_joint: {trajectory: 0.1, goal: 0.1}
      shoulder_lift_joint: {trajectory: 0.1, goal: 0.1}
      elbow_joint: {trajectory: 0.1, goal: 0.1}
      wrist_1_joint: {trajectory: 0.1, goal: 0.1}
      wrist_2_joint: {trajectory: 0.1, goal: 0.1}
      wrist_3_joint: {trajectory: 0.1, goal: 0.1}
      stop_trajectory_duration: 0.5
      state_publish_rate:  25
      action_monitor_rate: 10

   joint_group_position_controller:
      type: position_controllers/JointGroupPositionController
      joints:
         - shoulder_pan_joint
         - shoulder_lift_joint
         - elbow_joint
         - wrist_1_joint
         - wrist_2_joint
         - wrist_3_joint

I am spawning the joint_group_position_controller. Gazebo gives the following error when i spawn the model:

[ INFO] [1595405626.600237404, 4443.217000000]: Loading gazebo_ros_control plugin
[ INFO] [1595405626.600315414, 4443.217000000]: Starting gazebo_ros_control plugin in namespace: /
[ERROR] [1595405626.706939033, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/shoulder_pan_joint
[ERROR] [1595405626.708111425, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/shoulder_lift_joint
[ERROR] [1595405626.709094808, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/elbow_joint
[ERROR] [1595405626.710438356, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/wrist_1_joint
[ERROR] [1595405626.711494056, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/wrist_2_joint
[ERROR] [1595405626.712441104, 4443.217000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/wrist_3_joint

The Error makes sense since i don't set any gains.

when I publish to the /joint_group_position_controller/command to set the joint positions the robot is moving. You can see in the graph below how it is moving when i set the position from 0 to 1.

how does gazebo or ros_control or whoever is behind calculate that?

Thanks!