Merge remote-tracking branch 'remotes/prusa/stable' into merill-merge

src/libslic3r/Config.hpp

@@ -1479,7 +1479,7 @@ public:
         	unsigned char new_value = 0;
         	if (item_str == "nil") {
         		if (NULLABLE)
-        			this->values.push_back(nil_value());
+                    new_value = nil_value();
         		else
                     throw ConfigurationError("Deserializing nil into a non-nullable object");
         	} else if (item_str == "1") {

src/libslic3r/Optimize/Optimizer.hpp

@@ -8,6 +8,7 @@
 #include <functional>
 #include <limits>
 #include <cassert>
+#include <optional>
 
 namespace Slic3r { namespace opt {