cosmetic fixes for ros2param dump command. (#933)

* cosmetic fixes for ros2param dump command.

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

* pass through no parameters available case.

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

* bug fix from review comment.

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

* remove unnecessary initial assignment.

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

---------

Signed-off-by: Tomoya Fujita <Tomoya.Fujita@sony.com>

ros2param/ros2param/verb/dump.py

@@ -46,19 +46,6 @@ def add_arguments(self, parser, cli_name):  # noqa: D102
             '--timeout', metavar='N', type=int, default=1,
             help='Wait for N seconds until node becomes available (default %(default)s sec)')
 
-    @staticmethod
-    def get_parameter_values(node, node_name, params):
-        response = call_get_parameters(
-            node=node, node_name=node_name,
-            parameter_names=params)
-
-        # requested parameter not set
-        if not response.values:
-            return None
-
-        # extract type specific value
-        return [get_value(parameter_value=i) for i in response.values]
-
     def insert_dict(self, dictionary, key, value):
         split = key.split(PARAMETER_SEPARATOR_STRING, 1)
         if len(split) > 1:
@@ -80,7 +67,7 @@ def main(self, *, args):  # noqa: D102
         with DirectNode(args) as node:
             yaml_output = {node_name.full_name: {'ros__parameters': {}}}
 
-            # retrieve values
+            # retrieve parameter names
             response = call_list_parameters(node=node, node_name=absolute_node_name)
             if response is None:
                 print(
@@ -93,17 +80,26 @@ def main(self, *, args):  # noqa: D102
                     'Exception while calling list_parameters service of node '
                     f"'{node_name.full_name}': {e}", file=sys.stderr)
                 return
-
-            response = response.result().result.names
-            response = sorted(response)
-            parameter_values = self.get_parameter_values(node, absolute_node_name, response)
-            if parameter_values is None:
+            parameter_names = sorted(response.result().result.names)
+
+            # retrieve parameter values
+            response = None
+            try:
+                response = call_get_parameters(
+                    node=node, node_name=absolute_node_name, parameter_names=parameter_names)
+            except RuntimeError as e:
                 print(
                     'Exception while calling get_parameters service of node '
                     f"'{node_name.full_name}': {e}", file=sys.stderr)
                 return
-
-            for param_name, pval in zip(response, parameter_values):
+            if response.values is None:
+                # pass through here, no parameters are available with this node.
+                # since this is not failure, it proceeds to print the yaml as consistent behavior.
+                pass
+            parameter_values = [get_value(parameter_value=i) for i in response.values]
+
+            # create dictionary with parameter names and values
+            for param_name, pval in zip(parameter_names, parameter_values):
                 self.insert_dict(
                     yaml_output[node_name.full_name]['ros__parameters'], param_name, pval)