Merge pull request #8374 from obsidiansystems/improve-path-setting

Split `OptionalPathSetting` from `PathSetting`

src/libutil/experimental-features.hh

@@ -3,7 +3,7 @@
 
 #include "comparator.hh"
 #include "error.hh"
-#include "nlohmann/json_fwd.hpp"
+#include "json-utils.hh"
 #include "types.hh"
 
 namespace nix {
@@ -94,4 +94,10 @@ public:
 void to_json(nlohmann::json &, const ExperimentalFeature &);
 void from_json(const nlohmann::json &, ExperimentalFeature &);
 
+/**
+ * It is always rendered as a string
+ */
+template<>
+struct json_avoids_null<ExperimentalFeature> : std::true_type {};
+
 }