Properly handle a null abstract

app.py

@@ -47,12 +47,8 @@ class Work:
 
     @classmethod
     def from_dict(cls, d: dict) -> Self:
-        try:
-            inverted_index: dict[str, list[int]] = d["abstract_inverted_index"]
-        except KeyError:
-            abstract = None
-        else:
-            abstract = cls._recover_abstract(inverted_index)
+        inverted_index: None | dict[str, list[int]] = d["abstract_inverted_index"]
+        abstract = cls._recover_abstract(inverted_index) if inverted_index else None
 
         try:
             journal_name = d['primary_location']['source']['display_name']