proper KeyError handling in of

v6d2ctx/at_of.py

@@ -22,7 +22,7 @@ class AtOf(Generic[K, V]):
         def of(key: K) -> V:
             try:
                 return bucket[key]
-            except IndexError:
+            except (IndexError, KeyError):
                 raise Implicit
 
         return at, of