libcamera: yaml_parser: Return nullopt on error

The YamlParser::getList<>() function returns an std::optional<> to allow
callers to identify cases where parsing the .yaml file failed from cases
where the parsed list is just empty.

The current implementation returns a default constructed std::optional
in case of errors with

	return {};

The returned value is thus equal to std::nullopt, but the code can be
easily misinterpreted as returning an empty vector by a reader.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/yaml_parser.cpp

@@ -319,7 +319,7 @@ template<typename T,
 std::optional<std::vector<T>> YamlObject::getList() const
 {
 	if (type_ != Type::List)
-		return {};
+		return std::nullopt;
 
 	std::vector<T> values;
 	values.reserve(list_.size());
@@ -327,7 +327,7 @@ std::optional<std::vector<T>> YamlObject::getList() const
 	for (const YamlObject &entry : asList()) {
 		const auto value = entry.get<T>();
 		if (!value)
-			return {};
+			return std::nullopt;
 		values.emplace_back(*value);
 	}