[parser config] do not override whitespace with _undefined_str (#372)

* [parser config] do not override whitespace with `_undefined_str`

fixes #371

* [docs] include new contributor

* fix credits

Author: apalala

docs/contributors.rst

@@ -29,6 +29,7 @@ features, bug reports, bug fixes, or suggestions:
     `Karthikeyan Singaravelan`_,
     `Manuel Jacob`_,
     `Marcus Brinkmann`_,
+    `Matt Piekenbrock`_,
     `Mark Jason Dominus`_,
     `Max Liebkies`_,
     `Michael Noronha`_,

docs/links_contributors.rst

@@ -75,3 +75,4 @@
 .. _commonism: https://github.com/commonism
 .. _Vincent Fazio: https://github.com/vfazio
 .. _Benjamin Beasley: https://github.com/musicinmybrain
+.. _Matt Piekenbrock: https://github.com/peekxc

tatsu/infos.py

@@ -129,6 +129,9 @@ def _filter_non_init_fields(self, settings: MutableMapping[str, Any]) -> Mutable
         return settings
 
     def replace(self, **settings: Any) -> ParserConfig:
+        if settings.get('whitespace') is _undefined_str:
+            del settings['whitespace']
+        settings = dict(self._filter_non_init_fields(settings))
         overrides = self._filter_non_init_fields(self._find_common(**settings))
         result = dataclasses.replace(self, **overrides)
         if 'grammar' in overrides: