make default value of port optional, to allow empty strings

Author: facontidavide

include/behaviortree_cpp/basic_types.h

@@ -265,7 +265,7 @@ class PortInfo
 
   const std::string& description() const;
 
-  const std::string& defaultValue() const;
+  std::optional<std::string> defaultValue() const;
 
   bool isStronglyTyped() const
   {
@@ -282,7 +282,7 @@ class PortInfo
   std::type_index _type_info;
   StringConverter _converter;
   std::string description_;
-  std::string default_value_;
+  std::optional<std::string> default_value_;
 };
 
 template <typename T = PortInfo::AnyTypeAllowed>

src/basic_types.cpp

@@ -356,7 +356,7 @@ const std::string& PortInfo::description() const
   return description_;
 }
 
-const std::string& PortInfo::defaultValue() const
+std::optional<std::string> PortInfo::defaultValue() const
 {
   return default_value_;
 }

src/xml_parsing.cpp

@@ -632,9 +632,9 @@ TreeNode::Ptr XMLParser::Pimpl::createNodeFromXML(const XMLElement* element,
       auto direction = port_info.direction();
       if (direction != PortDirection::OUTPUT &&
           config.input_ports.count(port_name) == 0 &&
-          port_info.defaultValue().empty() == false)
+          port_info.defaultValue())
       {
-        config.input_ports.insert({port_name, port_info.defaultValue()});
+        config.input_ports.insert({port_name, *port_info.defaultValue()});
       }
     }
 
@@ -867,9 +867,9 @@ std::string writeTreeNodesModelXML(const BehaviorTreeFactory& factory,
       {
         port_element->SetAttribute("type", BT::demangle(port_info.type()).c_str());
       }
-      if (!port_info.defaultValue().empty())
+      if (!port_info.defaultValue())
       {
-        port_element->SetAttribute("default", port_info.defaultValue().c_str());
+        port_element->SetAttribute("default", port_info.defaultValue()->c_str());
       }
 
       if (!port_info.description().empty())