Add default values when declaring parameters. Fixes build error on Ub…

[tdenewiler]

…untu 20.04/ROS2 Foxy.

[tdenewiler]

My environment:

• Linux Mint 20.1 (based on Ubuntu 20.04)
• ROS2 Foxy from apt packages

I ran into build errors this morning after merging in the latest from the ros2 branch. To re-create:

mkdir -p turtlebot3_simulations/src
cd turtlebot3_simulations/src
git clone https://github.com/ROBOTIS-GIT/turtlebot3_simulations.git
git checkout ros2
cd ../..
. /opt/ros/foxy/setup.bash
colcon build --symlink-install

In the target branch there are build errors of the form

--- stderr: turtlebot3_fake_node                                                                              
/home/user/turtlebot3_simulations/src/turtlebot3_simulations/turtlebot3_fake_node/src/turtlebot3_fake_node.cpp: In member function ‘void Turtlebot3Fake::init_parameters()’:
/home/user/turtlebot3_simulations/src/turtlebot3_simulations/turtlebot3_fake_node/src/turtlebot3_fake_node.cpp:75:60: error: no matching function for call to ‘Turtlebot3Fake::declare_parameter<std::string>(const char [19])’
   75 |   this->declare_parameter<std::string>("joint_states_frame");

In the source branch (from fork) those build errors do not happen.

[tdenewiler]

@ruffsl, the error I am seeing was introduced in 6d48b40c15a39918fb1899027726a173d3c83f6f. Are you seeing this build error? Do the changes in this PR still satisfy moving away from deprecated uses of declare_parameter?

[ruffsl]

I think the ros2 branch here tracks the master brach from ros/ros2. Looks like you might want to target the foxy branch of you'd like to build from foxy binaries.

[tdenewiler]

I do not get build errors with the foxy-devel branch. Thanks.