fs/AllocatedPath: make the nullptr_t constructor public

src/config/Block.cxx

@@ -118,7 +118,7 @@ ConfigBlock::GetPath(const char *name, const char *default_value) const
 		s = bp->value.c_str();
 	} else {
 		if (default_value == nullptr)
-			return AllocatedPath::Null();
+			return nullptr;
 
 		s = default_value;
 	}

src/config/ConfigGlobal.cxx

@@ -125,7 +125,7 @@ config_get_path(ConfigOption option)
 {
 	const auto *param = config_get_param(option);
 	if (param == nullptr)
-		return AllocatedPath::Null();
+		return nullptr;
 
 	return param->GetPath();
 }

src/config/ConfigGlobal.hxx

@@ -71,7 +71,7 @@ config_get_string(enum ConfigOption option,
 /**
  * Returns an optional configuration variable which contains an
  * absolute path.  If there is a tilde prefix, it is expanded.
- * Returns AllocatedPath::Null() if the value is not present.
+ * Returns nullptr if the value is not present.
  *
  * Throws #std::runtime_error on error.
  */

src/config/ConfigPath.cxx

@@ -86,7 +86,7 @@ ParsePath(const char *path)
 		if (*path == '\0')
 			return GetConfiguredHome();
 
-		AllocatedPath home = AllocatedPath::Null();
+		AllocatedPath home = nullptr;
 
 		if (*path == '/') {
 			home = GetConfiguredHome();
@@ -107,11 +107,11 @@ ParsePath(const char *path)
 		}
 
 		if (home.IsNull())
-			return AllocatedPath::Null();
+			return nullptr;
 
 		AllocatedPath path2 = AllocatedPath::FromUTF8Throw(path);
 		if (path2.IsNull())
-			return AllocatedPath::Null();
+			return nullptr;
 
 		return AllocatedPath::Build(home, path2);
 	} else if (!PathTraitsUTF8::IsAbsolute(path)) {