Make properties message field optional for block creation

Signed-off-by: Ivan Čukić <ivan.cukic@kdab.com>

core/include/gnuradio-4.0/Graph.hpp

@@ -8,8 +8,8 @@
 #include <gnuradio-4.0/PluginLoader.hpp>
 #include <gnuradio-4.0/Port.hpp>
 #include <gnuradio-4.0/Sequence.hpp>
-#include <gnuradio-4.0/meta/typelist.hpp>
 #include <gnuradio-4.0/meta/reflection.hpp>
+#include <gnuradio-4.0/meta/typelist.hpp>
 #include <gnuradio-4.0/thread/thread_pool.hpp>
 
 #include <algorithm>
@@ -248,7 +248,13 @@ class Graph : public gr::Block<Graph> {
         const auto&         data       = message.data.value();
         const std::string&  type       = std::get<std::string>(data.at("type"s));
         const std::string&  parameters = std::get<std::string>(data.at("parameters"s));
-        const property_map& properties = std::get<property_map>(data.at("properties"s));
+        const property_map& properties = [&] {
+            if (auto it = data.find("properties"s); it != data.end()) {
+                return std::get<property_map>(it->second);
+            } else {
+                return property_map{};
+            }
+        }();
 
         auto& newBlock = emplaceBlock(type, parameters, properties);
 
@@ -281,7 +287,13 @@ class Graph : public gr::Block<Graph> {
         const std::string&  uniqueName = std::get<std::string>(data.at("uniqueName"s));
         const std::string&  type       = std::get<std::string>(data.at("type"s));
         const std::string&  parameters = std::get<std::string>(data.at("parameters"s));
-        const property_map& properties = std::get<property_map>(data.at("properties"s));
+        const property_map& properties = [&] {
+            if (auto it = data.find("properties"s); it != data.end()) {
+                return std::get<property_map>(it->second);
+            } else {
+                return property_map{};
+            }
+        }();
 
         auto it = std::ranges::find_if(_blocks, [&uniqueName](const auto& block) { return block->uniqueName() == uniqueName; });
         if (it == _blocks.end()) {