diff --git a/lib/src/codecs/text/encoder.dart b/lib/src/codecs/text/encoder.dart
index 9db671e..931c55e 100644
--- a/lib/src/codecs/text/encoder.dart
+++ b/lib/src/codecs/text/encoder.dart
@@ -285,7 +285,7 @@ class RecurrenceRuleToTextEncoder extends Converter<RecurrenceRule, String> {
           variant: InOnVariant.also,
           combination: ListCombination.disjunctive,
         ),
-    ].whereNotNull().toList();
+    ].nonNulls.toList();
     if (limits.isNotEmpty) {
       output.add(l10n.list(limits, ListCombination.conjunctiveLong));
     }
diff --git a/lib/src/iteration/date_set.dart b/lib/src/iteration/date_set.dart
index 8ece102..412a70b 100644
--- a/lib/src/iteration/date_set.dart
+++ b/lib/src/iteration/date_set.dart
@@ -1,4 +1,3 @@
-import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 import 'package:time/time.dart';
 
@@ -57,7 +56,7 @@ class DateSet {
   }
 
   Iterable<DateTime> get includedDates =>
-      start.until(end).map((i) => this[i]).whereNotNull();
+      start.until(end).map((i) => this[i]).nonNulls;
 }
 
 DateSet makeDateSet(RecurrenceRule rrule, DateTime base) {