Avoid returning loan when none was obtained. (ros2#1629)

Signed-off-by: Miguel Company <[email protected]>

Author: MiguelCompany

rclcpp/src/rclcpp/executor.cpp

@@ -610,16 +610,18 @@ Executor::execute_subscription(rclcpp::SubscriptionBase::SharedPtr subscription)
         return true;
       },
       [&]() {subscription->handle_loaned_message(loaned_msg, message_info);});
-    rcl_ret_t ret = rcl_return_loaned_message_from_subscription(
-      subscription->get_subscription_handle().get(),
-      loaned_msg);
-    if (RCL_RET_OK != ret) {
-      RCLCPP_ERROR(
-        rclcpp::get_logger("rclcpp"),
-        "rcl_return_loaned_message_from_subscription() failed for subscription on topic '%s': %s",
-        subscription->get_topic_name(), rcl_get_error_string().str);
+    if (nullptr != loaned_msg) {
+      rcl_ret_t ret = rcl_return_loaned_message_from_subscription(
+        subscription->get_subscription_handle().get(),
+        loaned_msg);
+      if (RCL_RET_OK != ret) {
+        RCLCPP_ERROR(
+          rclcpp::get_logger("rclcpp"),
+          "rcl_return_loaned_message_from_subscription() failed for subscription on topic '%s': %s",
+          subscription->get_topic_name(), rcl_get_error_string().str);
+      }
+      loaned_msg = nullptr;
     }
-    loaned_msg = nullptr;
   } else {
     // This case is taking a copy of the message data from the middleware via
     // inter-process communication.