Can't get double parameter in node (C++)

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I have a launch file with:

  <arg name="INTENSITY" default="1.2" />
  <param name="my_intensity" type="double" value="$(arg INTENSITY)" />

The same launch file starts a ROS node, my_node . In my_node's main method I have the following, to get that parameter:

  ros::init(argc, argv, "my_node");
  ros::NodeHandle nh;
  string param_name;
  if(!nh.searchParam("/my_intensity", param_name) ){
    ROS_ERROR("Can't find param.");
    return -1;
  }

  double it;
  ros::param::get(param_name, it);  

  ROS_INFO("Intensity is %f.", it);
  ...

Running this prints Intensity is 0.0.. Although when I run rosparam get /my_intensity in a terminal window I get the correct value (1.2).

When I change the type of it to string, what I get is an empty string. The same approach always worked for my other nodes. So I am really confused. What may be causing this behavior?

Thank you.

System: Ubuntu 16.04, ros-kinetic.