Implement None check for ComposableNodeContainer (#341) (#371)

(cherry picked from commit 35b2ca9)

Co-authored-by: methylDragon <[email protected]>

launch_ros/launch_ros/actions/composable_node_container.py

@@ -80,9 +80,11 @@ def execute(self, context: LaunchContext) -> Optional[List[Action]]:
         """
         load_actions = None  # type: Optional[List[Action]]
         valid_composable_nodes = []
-        for node_object in self.__composable_node_descriptions:
-            if node_object.condition() is None or node_object.condition().evaluate(context):
-                valid_composable_nodes.append(node_object)
+        if self.__composable_node_descriptions:
+            for node_object in self.__composable_node_descriptions:
+                if node_object.condition() is None or node_object.condition().evaluate(context):
+                    valid_composable_nodes.append(node_object)
+
         if (
             valid_composable_nodes is not None and
             len(valid_composable_nodes) > 0

test_launch_ros/test/test_launch_ros/actions/test_composable_node_container.py

@@ -89,6 +89,22 @@ def test_composable_node_container_empty_list_of_nodes():
     assert get_node_name_count(context, f'/{TEST_NODE_NAMESPACE}/{TEST_NODE_NAME}') == 0
 
 
+def test_composable_node_container_no_list_of_nodes():
+    """Test launching a ComposableNodeContainer with no passed in list of nodes."""
+    actions = [
+        ComposableNodeContainer(
+            package='rclcpp_components',
+            executable='component_container',
+            name=TEST_CONTAINER_NAME,
+            namespace=TEST_CONTAINER_NAMESPACE
+        ),
+    ]
+
+    context = _assert_launch_no_errors(actions)
+    assert get_node_name_count(context, f'/{TEST_CONTAINER_NAMESPACE}/{TEST_CONTAINER_NAME}') == 1
+    assert get_node_name_count(context, f'/{TEST_NODE_NAMESPACE}/{TEST_NODE_NAME}') == 0
+
+
 def test_composable_node_container_in_group_with_launch_configuration_in_description():
     """
     Test launch configuration is passed to ComposableNode description inside GroupAction.