Can' t load my xacro file in Gazebo correctly

edit

Hello All , I' m trying to simulate a simple car in Gazebo and for that I run into 2 errors:

[ERROR] [1599638879.847083135]: No link elements found in urdf file
[robot_state_publisher-4] process has died [pid 17398, exit code 1, cmd /opt/ros/noetic/lib/robot_state_publisher/robot_state_publisher __name:=robot_state_publisher __log:=/home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/robot_state_publisher-4.log].
log file: /home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/robot_state_publisher-4*.log
[gazebo-1] process has died [pid 17387, exit code 255, cmd /opt/ros/noetic/lib/gazebo_ros/gzserver -e ode worlds/empty.world __name:=gazebo __log:=/home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/gazebo-1.log].
log file: /home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/gazebo-1*.log

and this one:

[ERROR] [1599638890.694251, 978.255000]: Spawn service failed. Exiting.
[urdf_spawner-5] process has died [pid 17399, exit code 1, cmd /opt/ros/noetic/lib/gazebo_ros/spawn_model -urdf -model mrobot -param robot_description __name:=urdf_spawner __log:=/home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/urdf_spawner-5.log].
log file: /home/lilrookie76/.ros/log/4e57d700-f271-11ea-9781-711d86005210/urdf_spawner-5*.log

this is my launch file:

<launch>

    <arg name="paused" default="false"/>
    <arg name="use_sim_time" default="true"/>
    <arg name="gui" default="true"/>
    <arg name="headless" default="false"/>
    <arg name="debug" default="false"/>

    <include file="$(find gazebo_ros)/launch/empty_world.launch">
        <arg name="debug" value="$(arg debug)" />
        <arg name="gui" value="$(arg gui)" />
        <arg name="paused" value="$(arg paused)"/>
        <arg name="use_sim_time" value="$(arg use_sim_time)"/>
        <arg name="headless" value="$(arg headless)"/>
    </include>

    <param name="robot_description" command="$(find xacro)/xacro --inorder '$(find mbot_description)/urdf/mbot_gazebo.xacro'" /> 

    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" ></node> 

    <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher"  output="screen" >
        <param name="publish_frequency" type="double" value="50.0" />
    </node>

    <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
          args="-urdf -model mrobot -param robot_description"/> 

</launch>

these are related xacro files:

<?xml version="1.0"?>
<robot name="mbot" xmlns:xacro="http://www.ros.org/wiki/xacro">
    <xacro:include filename="$(find mbot_description)/urdf/mbot_base_gazebo.xacro" />
    <mbot_base_gazebo/>
</robot>

include this

<?xml version="1.0"?>
<robot name="mbot" xmlns:xacro="http://www.ros.org/wiki/xacro">

    <!-- PROPERTY LIST -->
    <xacro:property name="M_PI" value="3.1415926"/>
    <xacro:property name="base_mass"   value="1" /> 
    <xacro:property name="base_radius" value="0.20"/>
    <xacro:property name="base_length" value="0.16"/>

    <xacro:property name="wheel_mass"   value="0.2" />
    <xacro:property name="wheel_radius" value="0.06"/>
    <xacro:property name="wheel_length" value="0.025"/>
    <xacro:property name="wheel_joint_y" value="0.19"/>
    <xacro:property name="wheel_joint_z" value="0.05"/>

    <xacro:property name="caster_mass"    value="0.2" /> 
    <xacro:property name="caster_radius"  value="0.015"/> <!-- wheel_radius - ( base_length/2 - wheel_joint_z) -->
    <xacro:property name="caster_joint_x" value="0.18"/>

    <!-- Defining the colors used in this robot -->
    <material name="yellow">
        <color rgba="1 0.4 0 1"/>
    </material>
    <material name="black">
        <color rgba="0 0 0 0.95"/>
    </material> ...