message: Simplify use of argument `paused`
  ... avoiding code duplication
diff: <include file="$(find gazebo_ros)/launch/empty_world.launch" if="$(arg gazebo)">
  <arg name="world_name" value="$(arg world)"/>
  + <!-- Always start in paused mode, and only unpause when spawning the model -->
  <arg name="paused" value="true"/>
  <arg name="gui" value="$(eval not arg('headless'))"/>
  <arg name="use_sim_time" value="true"/>
  <param name="m_ee" value="0.76" if="$(arg use_gripper)" />
  + <arg name="unpause" value="$(eval '' if arg('paused') else '-unpause')" />
  <node name="$(arg arm_id)_model_spawner"
  pkg="gazebo_ros"
  type="spawn_model"
  - if="$(arg paused)"
  - args="-param robot_description -urdf -model $(arg arm_id)
  + args="-param robot_description -urdf -model $(arg arm_id) $(arg unpause)
  $(arg initial_joint_positions)
  - ">
  - </node>
  - <node name="$(arg arm_id)_model_spawner"
  - pkg="gazebo_ros"
  - type="spawn_model"
  - unless="$(arg paused)"
  - args="-param robot_description -urdf -model $(arg arm_id) -unpause
  - $(arg initial_joint_positions)
  - ">
  - </node>
  -
  + "/>
  <!-- Spawn required ROS controllers -->
  <node pkg="controller_manager"
  