err when running custom ROS controller

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I am trying to implement a custom ros_control effort controller.

As a first step, I created a copy of the effort_controllers package from the ros_controllers repo. Then I only kept the JointPositionController(https://github.com/ros-controls/ros_c...) and just renamed it to MyJointPositionController (both the C++ class and the plugin stuff). The code builds fine...

Then, in my config file I replaced effort_controllers/JointPositionController with effort_controllers/MyJointPositionController. However, when I spawn the controller I get the following error:

gzserver: /opt/ros/melodic/include/hardware_interface/joint_command_interface.h:60: void hardware_interface::JointHandle::setCommand(double): Assertion `cmd_' failed. Aborted (core dumped)

I am in ROS Melodic on Ubuntu 18.04.

Any idea what might be going wrong?