rviz does not display the urdf model after running the launch file

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My System Specifications ##

1. Oracle VirtualBox
   
2. Ubuntu 18.04
   
3. ROS Melodic 1.14.3
   
4. Host Computer- Windows 10 with Intel i7 and Nvidia 1660 graphics
   

I have been following the tutorials in the book "Mastering ROS for Robotics Programming" by Lentin Joseph. In chapter 2, for URDF tutorial, I did exactly follow the steps mentioned.

STEPS

1. I created my pan & tilt model package inside the 'src' folder in my catkin workspace.
   ~/catkin_ws/src $ catkin_create_pkg pan_tilt_model roscpp rospy tf geometry_msgs urdf rviz xacro
2. Inside the pan_tilt_model package, I created three new folders, namely 'launch', 'meshes' and 'urdf'.
   ~/catkin_ws/src/pan_tilt_model $ mkdir meshes launch urdf
3. Inside the 'urdf' folder, I created my URDF file named 'pan_tilt.urdf'
   ~/catkin_ws/src/pan_tilt_model/urdf $ gedit pan_tilt.urdf
4. Inside the 'launch' folder, I create my launch file named 'pan_tilt.launch'
   ~/catkin_ws/src/pan_tilt_model/launch $ gedit pan_tilt.launch
5. I tried to run the 'roslaunch' command to run the launch file for the pan & tilt model
   ~/catkin_ws $ roslaunch pan_tilt_model pan_tilt.launch

Expected Outcome

Rviz should display my pan & tilt model in its display area along with a joint_state_publisher GUI.

Outcome I got

Rviz didn't display my model in its canvas. It just displayed a blank grid. Also, rviz was showing errors as

• Global Status: Error
  
• Fixed Frame- Fixed Frame [map] does not exist.

I have attached the screenshot the rviz window I am getting in the below link. rviz_window

Launch File 'pan_tilt.urdf'

<launch>
<arg name="model" />
<!-- Parsing xacro and setting robot_description parameter -->
<param name="robot_description" textfile="$(find pan_tilt_model)/urdf/pan_tilt.urdf" />

<!-- Setting gui parameter to true for display joint slider -->

<!-- Starting Joint state publisher node which will publish the joint values -->

<!-- Starting robot state publish which will publish tf -->
<node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher" />
<!-- Launch visualization in rviz -->
<node name="rviz" pkg="rviz" type="rviz" args="-d $(find pan_tilt_model)/urdf.rviz" required="true" />
    <node name="jsp_gui" pkg="joint_state_publisher_gui" type="joint_state_publisher_gui" />
</launch>

URDF File 'pan_tilt.urdf'

<?xml version="1.0"?>
<robot name="pan_tilt">

  <link name="dummy">
   </link>

  <joint name="dummy_joint" type="fixed">
     <parent link="dummy"/>
     <child link="base_link"/>
   </joint>

  <link name="base_link">

    <visual>
      <geometry>
    <cylinder length="0.01" radius="0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <material name="yellow">
        <color rgba="1 1 0 1"/>
      </material>
    </visual>

    <collision>
      <geometry>
    <cylinder length="0.03" radius="0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0"/>
    </collision>
    <inertial>
    <mass value="1"/>
    <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
    </inertial>
  </link>

  <joint name="pan_joint" type="revolute">
    <parent link="base_link"/>
    <child link="pan_link"/>
    <origin xyz="0 0 0.1"/>
    <axis xyz="0 0 1" />
    <limit effort="300" velocity="0.1" lower="-3 ...