Update src/array/growable/dictionary.rs

Co-authored-by: Jorge Leitao <[email protected]>

src/array/growable/dictionary.rs

@@ -100,6 +100,7 @@ impl<'a, T: DictionaryKey> Growable<'a> for GrowableDictionary<'a, T> {
         self.key_values.extend(
             values
                 .iter()
+                // `.unwrap_or(0)` because this operation does not check for null values, which may contain any key.
                 .map(|x| T::from_usize(offset + x.to_usize().unwrap_or(0)).unwrap()),
         );
     }