Improve error message if ComposableNodeContainer 'name' or 'namespace…

…' arg is None (#191)

* Add error message if ComposableNodeContainer 'namespace' arg is None

This restores the original behavior in Eloquent and Foxy, but with an improved error message.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Improve error message for no node name

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

launch_ros/launch_ros/actions/composable_node_container.py

@@ -77,7 +77,13 @@ def __init__(
                 )
             namespace = node_namespace
 
-        if not namespace:
+        if name is None:
+            raise RuntimeError("'name' is a required argument")
+
+        if namespace is None:
+            raise RuntimeError("'namespace' is a required argument")
+
+        if namespace == '':
             namespace = '/'
         super().__init__(name=name, namespace=namespace, **kwargs)
         self.__composable_node_descriptions = composable_node_descriptions