message: FIX: Only instantiate Gazebo Tags for fingers if `hand` specified.
  Otherwise FrankaHWSim will try to setup HW interfaces for joints which are not
  in the URDF
diff: <xacro:if value="$(arg hand)">
  <xacro:hand ns="${arm_id}" rpy="0 0 ${-pi/4}" connected_to="${arm_id}_link8" />
  + <xacro:gazebo-joint joint="${arm_id}_finger_joint1" transmission="hardware_interface/EffortJointInterface" />
  + <xacro:gazebo-joint joint="${arm_id}_finger_joint2" transmission="hardware_interface/EffortJointInterface" />
  </xacro:if>
  <!-- Gazebo requires a joint to a link called "world" for statically mounted robots -->
  <xacro:gazebo-joint joint="${arm_id}_joint6" transmission="hardware_interface/EffortJointInterface" />
  <xacro:gazebo-joint joint="${arm_id}_joint7" transmission="hardware_interface/EffortJointInterface" />
  - <xacro:gazebo-joint joint="${arm_id}_finger_joint1" transmission="hardware_interface/EffortJointInterface" />
  - <xacro:gazebo-joint joint="${arm_id}_finger_joint2" transmission="hardware_interface/EffortJointInterface" />
  -
  <xacro:transmission-franka-state arm_id="${arm_id}" />
  <xacro:transmission-franka-model arm_id="${arm_id}"
  root="${arm_id}_joint1"
  