Invalid <param> tag: Cannot load command parameter [robot_description]:

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I am using ROS Kinetic and Ubuntu 16.04 I am following this tutorial for adding ar tag in gazebo: https://www.youtube.com/watch?v=WDhIa...

When I run roslaunch multi_scenario_robot spawn_ar_track_jr.launch I get this

cat: '$(arg': No such file or directory
cat: urdf_robot_file: No such file or directory
while processing /home/filip/catkin_ws/src/multi_robot_scenario/launch/spawn_robot_urdf_jr.launch:
Invalid <param> tag: Cannot load command parameter [robot_description]: command [cat $(arg urdf_robot_file] returned with code [1]. 
Param xml is param command="cat $(arg urdf_robot_file)" name="robot_description"/> The traceback for the exception was written to the log file

My launch file is:

<launch>

<arg name="x" default="0.0" />
<arg name="y" default="0.5" />
<arg name="z" default="0.5" />
<arg name="roll" default="1.57" />
<arg name="pitch" default="0" />
<arg name="yaw" default="0" />

<arg name="urdf_robot_file" default="$(find multi_robot_scenario)/ar_tag_5.urdf" />
<arg name="robot_name" default="ar_5"/>

<include file="$(find multi_robot_scenario)/launch/spawn_robot_urdf_jr.launch">
    <arg name="x" value="$(arg x)"/>
    <arg name="y" value="$(arg y)"/>
    <arg name="z" value="$(arg z)"/>
    <arg name="pitch" value="$(arg pitch)"/>
    <arg name="roll" value="$(arg roll)"/>
    <arg name="yaw" value="$(arg yaw)"/>

    <arg name="urdf_robot_file" value="$(arg urdf_robot_file" />
    <arg name="robot_name" value="$(arg robot_name)" />
</include>

</launch>

And spawn_robot_urdf_jr.launch is:

<launch>

<arg name="x" default="0.0" />
<arg name="y" default="0.0" />
<arg name="z" default="0.0" />
<arg name="roll" default="0" />
<arg name="pitch" default="0" />
<arg name="yaw" default="0" />

<arg name="urdf_robot_file" default="" />
<arg name="robot_name" default="" />

<param name="robot_description" command="cat $(arg urdf_robot_file)" />

<node name="$(arg robot_name)_urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen" args="-urdf -x $(arg x) -y $(arg y) -z $(arg z) -R $(arg roll) -P $(arg pitch) -Y $(arg yaw) -model $(arg robot_name) -param robot_description"/>
</launch>

Can someone please help? I wasn't able to find out what to do.