Issues with ROS2 Crystal: first steps with "colcon tests" and the listener-talker demo

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I tried to work a bit on ROS2. It seems that I misused it and got some errors.

On a freshly installed Ubuntu 18.04 Virtual Machine, I installed ROS2 Crystal via Debian packages: https://index.ros.org/doc/ros2/Linux-...

Then, I followed the colcon tutorial: https://index.ros.org/doc/ros2/Colcon... . The following command lines were okay.

wget https://raw.githubusercontent.com/ros2/ros2/master/ros2.repos
vcs import ~/ros2_ws/src < ros2.repos

Then colcon build --symlink-install worked okay, but gave a bit of warning

Summary: 228 packages finished [26min 38s]
  3 packages had stderr output: qt_gui_cpp ros1_bridge rqt_gui_cpp

When I run colcon test, I got errors:

summary: 227 packages finished [12min 16s]
  1 package failed: ros2topic
  25 packages had stderr output: composition demo_nodes_cpp demo_nodes_cpp_native image_tools intra_process_demo logging_demo message_filters osrf_pycommon rcl rcl_action rclcpp rclcpp_action rclcpp_lifecycle rclpy rqt rviz_common rviz_default_plugins rviz_rendering rviz_rendering_tests test_cli test_cli_remapping test_communication test_rclcpp tf2_ros tlsf_cpp
  23 packages had test failures: composition demo_nodes_cpp demo_nodes_cpp_native image_tools intra_process_demo logging_demo message_filters rcl rcl_action rclcpp rclcpp_action rclcpp_lifecycle rclpy rviz_common rviz_default_plugins rviz_rendering rviz_rendering_tests test_cli test_cli_remapping test_communication test_rclcpp tf2_ros tlsf_cpp

After sourcing local_setup.bash, I tried the demo

ros2 run demo_nodes_cpp listener &ros2 run demo_nodes_cpp talker

The command line failed:

zhfu@ubuntu:~/ros2_ws$ ros2 run demo_nodes_cpp listener & ros2 run demo_nodes_cpp talker
[1] 10554
terminate called after throwing an instance of 'std::logic_error'
  what():  basic_string::_M_construct null not valid
terminate called after throwing an instance of 'std::logic_error'
  what():  basic_string::_M_construct null not valid
[1]+  Exit 250                ros2 run demo_nodes_cpp listener

Why did I get a logic error? Cam someone help diagnose the issue?