logger: use Logger* instead of Logger& to propagate signature using swig

See the comment in IfcLogger.h explaining this.

src/ifcparse/IfcFile.h

@@ -447,7 +447,7 @@ public:
 };
 
 #ifdef WITH_IFCXML
-IFC_PARSE_API IfcFile* parse_ifcxml(const std::string& filename, Logger& logger = Logger::Root());
+IFC_PARSE_API IfcFile* parse_ifcxml(const std::string& filename, Logger* logger = nullptr);
 #endif
 
 namespace impl {

src/ifcparse/IfcLogger.h

@@ -142,6 +142,13 @@ class IFC_PARSE_API Logger {
     const std::vector<log_message>& log_messages() const { return log_messages_; }
 };
 
+// SWIG couldn't represent `Logger::Root()` default value using Python,
+// so when translating signature it represents it just as `fn(*args)`, losing information about args.
+// Using `Logger * = nullptr` instead of `&Logger = Logger::Root` helps,
+// since `nullptr` is convertable Python's `None`.
+// `logger_or_root` is just covering the boilerplate for this pattern.
+inline Logger& logger_or_root(Logger* logger) { return logger ? *logger : Logger::Root(); }
+
 #define PERF(x)                                                      \
                                                                      \
     Logger::Root().Message(Logger::LOG_PERF, "SYS", 1, x);            \

src/ifcparse/parse_ifcxml.cpp

@@ -695,10 +695,10 @@ end:
     return;
 }
 
-IFC_PARSE_API IfcParse::IfcFile* IfcParse::parse_ifcxml(const std::string& filename, Logger& logger) {
+IFC_PARSE_API IfcParse::IfcFile* IfcParse::parse_ifcxml(const std::string& filename, Logger* logger) {
     throw std::runtime_error("IFC-XML import temporarily disabled");
 
-    ifcxml_parse_state state(logger);
+    ifcxml_parse_state state(logger_or_root(logger));
 
     xmlSAXHandler handler;
     memset(&handler, 0, sizeof(xmlSAXHandler));