refactor: PR feedback

Co-authored-by: Moritz E. Beber <midnighter@posteo.net>

Author: yt-ms

src/structurizr/view/view_set.py

@@ -391,5 +391,5 @@ def copy_layout_information_from(self, source: "ViewSet") -> None:
     def _ensure_key_is_specific_and_unique(self, key: str) -> None:
         if key is None or key == "":
             raise ValueError("A key must be specified.")
-        if self.get_view(key) is not None:
+        if key in self._views:
             raise ValueError(f"View already exists in workspace with key '{key}'.")