Fix NameSelector serialization (#704)

* fix NameSelector inversion

* Always set `_config_pos_init`

bsb/config/_make.py

@@ -57,6 +57,7 @@ def __call__(meta_subject, *args, _parent=None, _key=None, **kwargs):
             instance = meta_subject.__new__(
                 meta_subject, _parent=_parent, _key=_key, **kwargs
             )
+            instance._config_pos_init = getattr(instance, "_config_pos_init", False)
             # Call the end user's __init__ with the rewritten arguments, if one is defined
             if has_own_init:
                 sig = inspect.signature(instance.__init__)

bsb/morphologies/selector.py

@@ -33,6 +33,11 @@ def pick(self, morphology):
 class NameSelector(MorphologySelector, classmap_entry="by_name"):
     names = config.list(type=str, required=True)
 
+    def __inv__(self):
+        if self._config_pos_init:
+            return self.names[0]
+        return self.__tree__()
+
     def _cache_patterns(self):
         self._pnames = {n: n.replace("*", r".*").replace("|", "\\|") for n in self.names}
         self._patterns = {n: re.compile(f"^{pat}$") for n, pat in self._pnames.items()}