Fix None Toolchain (#63)

Author: Behemyth

cppython/schema.py

@@ -46,7 +46,10 @@ def validate_path(cls, value):  # pylint: disable=E0213
         """
         TODO
         """
-        return Path(value).as_posix()
+        if value is not None:
+            return Path(value).as_posix()
+
+        return None
 
 
 class BuildPreset(Preset):