Codechange: String parameters can now be explicitly not initialised.

As the visitor is now more complex this requires an unspecialised GetNextParameter() to avoid it being repeated for each return type.

src/strings_internal.h

@@ -83,6 +83,7 @@ public:
 	uint64_t GetNextParameter()
 	{
 		struct visitor {
+			uint64_t operator()(const std::monostate &) { throw std::out_of_range("Attempt to read uninitialised parameter as integer"); }
 			uint64_t operator()(const uint64_t &arg) { return arg; }
 			uint64_t operator()(const std::string &) { throw std::out_of_range("Attempt to read string parameter as integer"); }
 		};
@@ -113,11 +114,12 @@ public:
 	const char *GetNextParameterString()
 	{
 		struct visitor {
+			const char *operator()(const std::monostate &) { throw std::out_of_range("Attempt to read uninitialised parameter as string"); }
 			const char *operator()(const uint64_t &) { throw std::out_of_range("Attempt to read integer parameter as string"); }
 			const char *operator()(const std::string &arg) { return arg.c_str(); }
 		};
 
-		const auto &param = GetNextParameterReference();
+		const auto &param = this->GetNextParameterReference();
 		return std::visit(visitor{}, param.data);
 	}