diff --git a/packages/combinator/lib/src/combinator/advance.dart b/packages/combinator/lib/src/combinator/advance.dart
index 49fcdb88..01506dc2 100644
--- a/packages/combinator/lib/src/combinator/advance.dart
+++ b/packages/combinator/lib/src/combinator/advance.dart
@@ -8,7 +8,7 @@ class _Advance<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!.change(parser: this);
+    var result = parser._parse(args.increaseDepth()).change(parser: this);
     if (result.successful) args.scanner.position += amount;
     return result;
   }
diff --git a/packages/combinator/lib/src/combinator/any.dart b/packages/combinator/lib/src/combinator/any.dart
index 0c16a81d..616bf29d 100644
--- a/packages/combinator/lib/src/combinator/any.dart
+++ b/packages/combinator/lib/src/combinator/any.dart
@@ -8,7 +8,7 @@ part of lex.src.combinator;
 /// generate any error at all.
 Parser<T> any<T>(Iterable<Parser<T>> parsers,
     {bool backtrack: true, errorMessage, SyntaxErrorSeverity? severity}) {
-  return new _Any(parsers, backtrack != false, errorMessage,
+  return _Any(parsers, backtrack != false, errorMessage,
       severity ?? SyntaxErrorSeverity.error);
 }
 
@@ -26,14 +26,14 @@ class _Any<T> extends Parser<T> {
         .where((p) => !args.trampoline.isActive(p, args.scanner.position));
 
     if (inactive.isEmpty) {
-      return new ParseResult(args.trampoline, args.scanner, this, false, []);
+      return ParseResult(args.trampoline, args.scanner, this, false, []);
     }
 
     var errors = <SyntaxError>[];
     int replay = args.scanner.position;
 
     for (var parser in inactive) {
-      var result = parser._parse(args.increaseDepth())!;
+      var result = parser._parse(args.increaseDepth());
 
       if (result.successful)
         return result;
@@ -45,7 +45,7 @@ class _Any<T> extends Parser<T> {
 
     if (errorMessage != false) {
       errors.add(
-        new SyntaxError(
+        SyntaxError(
           severity,
           errorMessage?.toString() ??
               'No match found for ${parsers.length} alternative(s)',
@@ -54,13 +54,13 @@ class _Any<T> extends Parser<T> {
       );
     }
 
-    return new ParseResult(args.trampoline, args.scanner, this, false, errors);
+    return ParseResult(args.trampoline, args.scanner, this, false, errors);
   }
 
   @override
-  ParseResult<T>? __parse(ParseArgs args) {
+  ParseResult<T> __parse(ParseArgs args) {
     // Never called
-    return null;
+    throw ArgumentError("[Combinator] Invalid method call");
   }
 
   @override
diff --git a/packages/combinator/lib/src/combinator/cast.dart b/packages/combinator/lib/src/combinator/cast.dart
index 6bd44f80..bc7280ad 100644
--- a/packages/combinator/lib/src/combinator/cast.dart
+++ b/packages/combinator/lib/src/combinator/cast.dart
@@ -7,7 +7,7 @@ class _Cast<T, U extends T> extends Parser<U> {
 
   @override
   ParseResult<U> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!;
+    var result = parser._parse(args.increaseDepth());
     return new ParseResult<U>(
       args.trampoline,
       args.scanner,
@@ -38,7 +38,7 @@ class _CastDynamic<T> extends Parser<dynamic> {
 
   @override
   ParseResult<dynamic> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!;
+    var result = parser._parse(args.increaseDepth());
     return new ParseResult<dynamic>(
       args.trampoline,
       args.scanner,
diff --git a/packages/combinator/lib/src/combinator/chain.dart b/packages/combinator/lib/src/combinator/chain.dart
index 49cc8c1b..16af1658 100644
--- a/packages/combinator/lib/src/combinator/chain.dart
+++ b/packages/combinator/lib/src/combinator/chain.dart
@@ -18,7 +18,7 @@ class _Alt<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!;
+    var result = parser._parse(args.increaseDepth());
     return result.successful
         ? result
         : result.addErrors([
@@ -48,7 +48,7 @@ class _Chain<T> extends ListParser<T> {
     bool successful = true;
 
     for (var parser in parsers) {
-      var result = parser._parse(args.increaseDepth())!;
+      var result = parser._parse(args.increaseDepth());
 
       if (!result.successful) {
         if (parser is _Alt) errors.addAll(result.errors);
diff --git a/packages/combinator/lib/src/combinator/check.dart b/packages/combinator/lib/src/combinator/check.dart
index 58416040..a9bfcc63 100644
--- a/packages/combinator/lib/src/combinator/check.dart
+++ b/packages/combinator/lib/src/combinator/check.dart
@@ -11,7 +11,7 @@ class _Check<T> extends Parser<T> {
   @override
   ParseResult<T> __parse(ParseArgs args) {
     var matchState = {};
-    var result = parser._parse(args.increaseDepth())!.change(parser: this);
+    var result = parser._parse(args.increaseDepth()).change(parser: this);
     if (!result.successful)
       return result;
     else if (!matcher.matches(result.value, matchState)) {
diff --git a/packages/combinator/lib/src/combinator/combinator.dart b/packages/combinator/lib/src/combinator/combinator.dart
index 10cbaf5d..08e1349e 100644
--- a/packages/combinator/lib/src/combinator/combinator.dart
+++ b/packages/combinator/lib/src/combinator/combinator.dart
@@ -67,9 +67,9 @@ class ParseArgs {
 
 /// A parser combinator, which can parse very complicated grammars in a manageable manner.
 abstract class Parser<T> {
-  ParseResult<T>? __parse(ParseArgs args);
+  ParseResult<T> __parse(ParseArgs args);
 
-  ParseResult<T>? _parse(ParseArgs args) {
+  ParseResult<T> _parse(ParseArgs args) {
     var pos = args.scanner.position;
 
     if (args.trampoline.hasMemoized(this, pos))
@@ -86,7 +86,7 @@ abstract class Parser<T> {
   }
 
   /// Parses text from a [SpanScanner].
-  ParseResult<T>? parse(SpanScanner scanner, [int depth = 1]) {
+  ParseResult<T> parse(SpanScanner scanner, [int depth = 1]) {
     var args = ParseArgs(Trampoline(), scanner, depth);
     return _parse(args);
   }
@@ -105,7 +105,7 @@ abstract class Parser<T> {
 
   // TODO: Type issue
   /// Runs the given function, which changes the returned [ParseResult] into one relating to a [U] object.
-  Parser<U> change<U>(ParseResult<U> Function(ParseResult<T>?) f) {
+  Parser<U> change<U>(ParseResult<U> Function(ParseResult<T>) f) {
     return _Change<T, U>(this, f);
   }
 
@@ -140,8 +140,10 @@ abstract class Parser<T> {
   /// Ensures this pattern is not matched.
   ///
   /// You can provide an [errorMessage].
-  Parser<T> negate({String? errorMessage, SyntaxErrorSeverity? severity}) =>
-      _Negate<T>(this, errorMessage, severity ?? SyntaxErrorSeverity.error);
+  Parser<T> negate(
+          {String errorMessage = 'Negate error',
+          SyntaxErrorSeverity severity = SyntaxErrorSeverity.error}) =>
+      _Negate<T>(this, errorMessage, severity);
 
   /// Caches the results of parse attempts at various locations within the source text.
   ///
@@ -153,7 +155,7 @@ abstract class Parser<T> {
   /// Consumes `this` and another parser, but only considers the result of `this` parser.
   Parser<T> and(Parser other) => then(other).change<T>((r) {
         return ParseResult<T>(
-          r!.trampoline,
+          r.trampoline,
           r.scanner,
           this,
           r.successful,
@@ -176,7 +178,7 @@ abstract class Parser<T> {
   /// The generated parser only runs once; repeated uses always exit eagerly.
   Parser<T> safe(
           {bool backtrack: true,
-          String? errorMessage,
+          String errorMessage = "error",
           SyntaxErrorSeverity? severity}) =>
       _Safe<T>(
           this, backtrack, errorMessage, severity ?? SyntaxErrorSeverity.error);
@@ -240,7 +242,7 @@ abstract class Parser<T> {
   Parser<T> space() => trail(RegExp(r'[ \n\r\t]+'));
 
   /// Consumes 0 or more instance(s) of this parser.
-  ListParser<T?> star({bool backtrack: true}) =>
+  ListParser<T> star({bool backtrack: true}) =>
       times(1, exact: false, backtrack: backtrack).opt();
 
   /// Shortcut for [chain]-ing two parsers together.
@@ -259,10 +261,10 @@ abstract class Parser<T> {
   /// an infinite amount of occurrences after the specified [count].
   ///
   /// You can provide custom error messages for when there are [tooFew] or [tooMany] occurrences.
-  ListParser<T?> times(int count,
+  ListParser<T> times(int count,
       {bool exact: true,
-      String? tooFew,
-      String? tooMany,
+      String tooFew = 'Too few',
+      String tooMany = 'Too many',
       bool backtrack: true,
       SyntaxErrorSeverity? severity}) {
     return _Repeat<T>(this, count, exact, tooFew, tooMany, backtrack,
diff --git a/packages/combinator/lib/src/combinator/compare.dart b/packages/combinator/lib/src/combinator/compare.dart
index 49a39701..44a1ddd2 100644
--- a/packages/combinator/lib/src/combinator/compare.dart
+++ b/packages/combinator/lib/src/combinator/compare.dart
@@ -8,7 +8,7 @@ class _Compare<T> extends ListParser<T> {
 
   @override
   ParseResult<List<T>> __parse(ParseArgs args) {
-    ParseResult<List<T>> result = parser._parse(args.increaseDepth())!;
+    ParseResult<List<T>> result = parser._parse(args.increaseDepth());
     if (!result.successful) return result;
 
     result = result.change(
diff --git a/packages/combinator/lib/src/combinator/fold_errors.dart b/packages/combinator/lib/src/combinator/fold_errors.dart
index 5b838e6f..6d15c69a 100644
--- a/packages/combinator/lib/src/combinator/fold_errors.dart
+++ b/packages/combinator/lib/src/combinator/fold_errors.dart
@@ -8,7 +8,7 @@ class _FoldErrors<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!.change(parser: this);
+    var result = parser._parse(args.increaseDepth()).change(parser: this);
     var errors = result.errors.fold<List<SyntaxError>>([], (out, e) {
       if (!out.any((b) => equal(e, b))) out.add(e);
       return out;
diff --git a/packages/combinator/lib/src/combinator/index.dart b/packages/combinator/lib/src/combinator/index.dart
index a3791333..6eb9eaf8 100644
--- a/packages/combinator/lib/src/combinator/index.dart
+++ b/packages/combinator/lib/src/combinator/index.dart
@@ -8,7 +8,7 @@ class _Index<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    ParseResult<List<T>> result = parser._parse(args.increaseDepth())!;
+    ParseResult<List<T>> result = parser._parse(args.increaseDepth());
     Object? value;
 
     if (result.successful)
diff --git a/packages/combinator/lib/src/combinator/longest.dart b/packages/combinator/lib/src/combinator/longest.dart
index ae00c2c8..7028bd16 100644
--- a/packages/combinator/lib/src/combinator/longest.dart
+++ b/packages/combinator/lib/src/combinator/longest.dart
@@ -31,7 +31,7 @@ class _Longest<T> extends Parser<T> {
     var results = <ParseResult<T>>[];
 
     for (var parser in inactive) {
-      var result = parser._parse(args.increaseDepth())!;
+      var result = parser._parse(args.increaseDepth());
 
       if (result.successful && result.span != null)
         results.add(result);
@@ -66,7 +66,7 @@ class _Longest<T> extends Parser<T> {
     var results = <ParseResult<T>>[];
 
     for (var parser in parsers) {
-      var result = parser._parse(args.increaseDepth())!;
+      var result = parser._parse(args.increaseDepth());
 
       if (result.successful)
         results.add(result);
diff --git a/packages/combinator/lib/src/combinator/map.dart b/packages/combinator/lib/src/combinator/map.dart
index 37acddd5..4dfb326d 100644
--- a/packages/combinator/lib/src/combinator/map.dart
+++ b/packages/combinator/lib/src/combinator/map.dart
@@ -8,8 +8,8 @@ class _Map<T, U> extends Parser<U> {
 
   @override
   ParseResult<U> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!;
-    return new ParseResult<U>(
+    var result = parser._parse(args.increaseDepth());
+    return ParseResult<U>(
       args.trampoline,
       args.scanner,
       this,
@@ -34,7 +34,7 @@ class _Map<T, U> extends Parser<U> {
 
 class _Change<T, U> extends Parser<U> {
   final Parser<T> parser;
-  final ParseResult<U> Function(ParseResult<T>?) f;
+  final ParseResult<U> Function(ParseResult<T>) f;
 
   _Change(this.parser, this.f);
 
diff --git a/packages/combinator/lib/src/combinator/max_depth.dart b/packages/combinator/lib/src/combinator/max_depth.dart
index f9054132..1c28a9d2 100644
--- a/packages/combinator/lib/src/combinator/max_depth.dart
+++ b/packages/combinator/lib/src/combinator/max_depth.dart
@@ -7,7 +7,7 @@ class _MaxDepth<T> extends Parser<T> {
   _MaxDepth(this.parser, this.cap);
 
   @override
-  ParseResult<T>? __parse(ParseArgs args) {
+  ParseResult<T> __parse(ParseArgs args) {
     if (args.depth > cap) {
       return new ParseResult<T>(args.trampoline, args.scanner, this, false, []);
     }
diff --git a/packages/combinator/lib/src/combinator/negate.dart b/packages/combinator/lib/src/combinator/negate.dart
index 30a8c377..d49582d8 100644
--- a/packages/combinator/lib/src/combinator/negate.dart
+++ b/packages/combinator/lib/src/combinator/negate.dart
@@ -9,7 +9,7 @@ class _Negate<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!.change(parser: this);
+    var result = parser._parse(args.increaseDepth()).change(parser: this);
 
     if (!result.successful) {
       return new ParseResult<T>(
diff --git a/packages/combinator/lib/src/combinator/opt.dart b/packages/combinator/lib/src/combinator/opt.dart
index ac2b31c2..12083ed7 100644
--- a/packages/combinator/lib/src/combinator/opt.dart
+++ b/packages/combinator/lib/src/combinator/opt.dart
@@ -9,7 +9,7 @@ class _Opt<T> extends Parser<T> {
   @override
   ParseResult<T> __parse(ParseArgs args) {
     var replay = args.scanner.position;
-    var result = parser._parse(args.increaseDepth())!;
+    var result = parser._parse(args.increaseDepth());
 
     if (!result.successful) args.scanner.position = replay;
 
@@ -37,7 +37,7 @@ class _ListOpt<T> extends ListParser<T> {
   @override
   ParseResult<List<T>> __parse(ParseArgs args) {
     var replay = args.scanner.position;
-    ParseResult<List<T>> result = parser._parse(args.increaseDepth())!;
+    ParseResult<List<T>> result = parser._parse(args.increaseDepth());
 
     if (!result.successful) args.scanner.position = replay;
 
diff --git a/packages/combinator/lib/src/combinator/reduce.dart b/packages/combinator/lib/src/combinator/reduce.dart
index ae2d7d14..951da47b 100644
--- a/packages/combinator/lib/src/combinator/reduce.dart
+++ b/packages/combinator/lib/src/combinator/reduce.dart
@@ -8,7 +8,7 @@ class _Reduce<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    ParseResult<List<T>> result = parser._parse(args.increaseDepth())!;
+    ParseResult<List<T>> result = parser._parse(args.increaseDepth());
 
     if (!result.successful)
       return new ParseResult<T>(
diff --git a/packages/combinator/lib/src/combinator/reference.dart b/packages/combinator/lib/src/combinator/reference.dart
index dd2b6b9b..aefa32d3 100644
--- a/packages/combinator/lib/src/combinator/reference.dart
+++ b/packages/combinator/lib/src/combinator/reference.dart
@@ -16,22 +16,26 @@ class Reference<T> extends Parser<T> {
   }
 
   @override
-  ParseResult<T>? __parse(ParseArgs args) {
+  ParseResult<T> __parse(ParseArgs args) {
     if (_parser == null)
       throw new StateError('There is no parser assigned to this reference.');
     return _parser!._parse(args);
   }
 
   @override
-  ParseResult<T>? _parse(ParseArgs args) {
+  ParseResult<T> _parse(ParseArgs args) {
+    if (_parser == null)
+      throw new StateError('There is no parser assigned to this reference.');
     return _parser!._parse(args);
   }
 
   @override
   void stringify(CodeBuffer buffer) {
-    if (_parser == null)
+    if (_parser == null) {
       buffer.writeln('(undefined reference <$T>)');
-    else if (!printed) _parser!.stringify(buffer);
+    } else if (!printed) {
+      _parser!.stringify(buffer);
+    }
     printed = true;
     buffer.writeln('(previously printed reference)');
   }
diff --git a/packages/combinator/lib/src/combinator/repeat.dart b/packages/combinator/lib/src/combinator/repeat.dart
index be8b9c57..2ee452bd 100644
--- a/packages/combinator/lib/src/combinator/repeat.dart
+++ b/packages/combinator/lib/src/combinator/repeat.dart
@@ -1,63 +1,67 @@
 part of lex.src.combinator;
 
-class _Repeat<T> extends ListParser<T?> {
+class _Repeat<T> extends ListParser<T> {
   final Parser<T> parser;
   final int count;
   final bool exact, backtrack;
-  final String? tooFew, tooMany;
+  final String tooFew;
+  final String tooMany;
   final SyntaxErrorSeverity severity;
 
   _Repeat(this.parser, this.count, this.exact, this.tooFew, this.tooMany,
       this.backtrack, this.severity);
 
   @override
-  ParseResult<List<T?>> __parse(ParseArgs args) {
+  ParseResult<List<T>> __parse(ParseArgs args) {
     var errors = <SyntaxError>[];
-    var results = <T?>[];
-    var spans = <FileSpan?>[];
+    var results = <T>[];
+    var spans = <FileSpan>[];
     int success = 0, replay = args.scanner.position;
     ParseResult<T>? result;
 
     do {
       result = parser._parse(args.increaseDepth());
-      if (result!.successful) {
+      if (result.successful) {
         success++;
-        results.add(result.value);
+        if (result.value != null) {
+          results.add(result.value!);
+        }
         replay = args.scanner.position;
       } else if (backtrack) args.scanner.position = replay;
 
-      if (result.span != null) spans.add(result.span);
+      if (result.span != null) {
+        spans.add(result.span!);
+      }
     } while (result.successful);
 
     if (success < count) {
       errors.addAll(result.errors);
       errors.add(
-        new SyntaxError(
+        SyntaxError(
           severity,
-          tooFew ?? 'Expected at least $count occurence(s).',
+          tooFew,
           result.span ?? args.scanner.emptySpan,
         ),
       );
 
       if (backtrack) args.scanner.position = replay;
 
-      return new ParseResult<List<T?>>(
+      return ParseResult<List<T>>(
           args.trampoline, args.scanner, this, false, errors);
     } else if (success > count && exact) {
       if (backtrack) args.scanner.position = replay;
 
-      return new ParseResult<List<T?>>(
-          args.trampoline, args.scanner, this, false, [
-        new SyntaxError(
+      return ParseResult<List<T>>(args.trampoline, args.scanner, this, false, [
+        SyntaxError(
           severity,
-          tooMany ?? 'Expected no more than $count occurence(s).',
+          tooMany,
           result.span ?? args.scanner.emptySpan,
         ),
       ]);
     }
 
-    var span = spans.reduce((a, b) => a!.expand(b!));
-    return new ParseResult<List<T?>>(
+    var span = spans.reduce((a, b) => a.expand(b));
+    return ParseResult<List<T>>(
       args.trampoline,
       args.scanner,
       this,
@@ -70,7 +74,7 @@ class _Repeat<T> extends ListParser<T?> {
 
   @override
   void stringify(CodeBuffer buffer) {
-    var r = new StringBuffer('{$count');
+    var r = StringBuffer('{$count');
     if (!exact) r.write(',');
     r.write('}');
     buffer
diff --git a/packages/combinator/lib/src/combinator/safe.dart b/packages/combinator/lib/src/combinator/safe.dart
index 8bac100e..6820d3ee 100644
--- a/packages/combinator/lib/src/combinator/safe.dart
+++ b/packages/combinator/lib/src/combinator/safe.dart
@@ -3,14 +3,14 @@ part of lex.src.combinator;
 class _Safe<T> extends Parser<T> {
   final Parser<T> parser;
   final bool backtrack;
-  final String? errorMessage;
+  final String errorMessage;
   final SyntaxErrorSeverity severity;
   bool _triggered = false;
 
   _Safe(this.parser, this.backtrack, this.errorMessage, this.severity);
 
   @override
-  ParseResult<T>? __parse(ParseArgs args) {
+  ParseResult<T> __parse(ParseArgs args) {
     var replay = args.scanner.position;
 
     try {
@@ -21,16 +21,13 @@ class _Safe<T> extends Parser<T> {
       if (backtrack) args.scanner.position = replay;
       var errors = <SyntaxError>[];
 
-      if (errorMessage != null) {
-        // TODO: Custom severity for all errors?
-        errors.add(
-          new SyntaxError(
-            severity,
-            errorMessage,
-            args.scanner.lastSpan ?? args.scanner.emptySpan,
-          ),
-        );
-      }
+      errors.add(
+        new SyntaxError(
+          severity,
+          errorMessage,
+          args.scanner.lastSpan ?? args.scanner.emptySpan,
+        ),
+      );
 
       return new ParseResult<T>(
           args.trampoline, args.scanner, this, false, errors);
diff --git a/packages/combinator/lib/src/combinator/to_list.dart b/packages/combinator/lib/src/combinator/to_list.dart
index a339db50..a73fa954 100644
--- a/packages/combinator/lib/src/combinator/to_list.dart
+++ b/packages/combinator/lib/src/combinator/to_list.dart
@@ -7,7 +7,7 @@ class _ToList<T> extends ListParser<T?> {
 
   @override
   ParseResult<List<T?>> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!;
+    var result = parser._parse(args.increaseDepth());
 
     if (result.value is List) {
       return (result as ParseResult<List<T?>>).change(parser: this);
diff --git a/packages/combinator/lib/src/combinator/value.dart b/packages/combinator/lib/src/combinator/value.dart
index ab206187..b0612073 100644
--- a/packages/combinator/lib/src/combinator/value.dart
+++ b/packages/combinator/lib/src/combinator/value.dart
@@ -8,7 +8,7 @@ class _Value<T> extends Parser<T> {
 
   @override
   ParseResult<T> __parse(ParseArgs args) {
-    var result = parser._parse(args.increaseDepth())!.change(parser: this);
+    var result = parser._parse(args.increaseDepth()).change(parser: this);
     return result.successful ? result.change(value: f(result)) : result;
   }
 
diff --git a/packages/combinator/test/list_test.dart b/packages/combinator/test/list_test.dart
index 64bf8fba..26b0333e 100644
--- a/packages/combinator/test/list_test.dart
+++ b/packages/combinator/test/list_test.dart
@@ -12,11 +12,11 @@ main() {
 
   test('sort', () {
     var parser = numbers.sort((a, b) => a!.compareTo(b!));
-    expect(parser.parse(scan('21,2,3,34,20'))!.value, [2, 3, 20, 21, 34]);
+    expect(parser.parse(scan('21,2,3,34,20')).value, [2, 3, 20, 21, 34]);
   });
   test('reduce', () {
     var parser = numbers.reduce((a, b) => a! + b!);
-    expect(parser.parse(scan('21,2,3,34,20'))!.value, 80);
-    expect(parser.parse(scan('not numbers'))!.value, isNull);
+    expect(parser.parse(scan('21,2,3,34,20')).value, 80);
+    expect(parser.parse(scan('not numbers')).value, isNull);
   });
 }
diff --git a/packages/combinator/test/match_test.dart b/packages/combinator/test/match_test.dart
index d1406276..60504d93 100644
--- a/packages/combinator/test/match_test.dart
+++ b/packages/combinator/test/match_test.dart
@@ -4,13 +4,13 @@ import 'common.dart';
 
 main() {
   test('match string', () {
-    expect(match('hello').parse(scan('hello world'))!.successful, isTrue);
+    expect(match('hello').parse(scan('hello world')).successful, isTrue);
   });
   test('match start only', () {
-    expect(match('hello').parse(scan('goodbye hello'))!.successful, isFalse);
+    expect(match('hello').parse(scan('goodbye hello')).successful, isFalse);
   });
 
   test('fail if no match', () {
-    expect(match('hello').parse(scan('world'))!.successful, isFalse);
+    expect(match('hello').parse(scan('world')).successful, isFalse);
   });
 }
diff --git a/packages/combinator/test/misc_test.dart b/packages/combinator/test/misc_test.dart
index f90d5d83..b3a141f9 100644
--- a/packages/combinator/test/misc_test.dart
+++ b/packages/combinator/test/misc_test.dart
@@ -14,29 +14,29 @@ main() {
   });
 
   test('change', () {
-    var parser = match('hello').change((r) => r!.change(value: 23));
-    expect(parser.parse(scan('helloworld'))!.value, 23);
+    var parser = match('hello').change((r) => r.change(value: 23));
+    expect(parser.parse(scan('helloworld')).value, 23);
   });
 
   test('check', () {
     var parser = match<int>(new RegExp(r'[A-Za-z]+'))
         .value((r) => r.span!.length)
         .check(greaterThan(3));
-    expect(parser.parse(scan('helloworld'))!.successful, isTrue);
-    expect(parser.parse(scan('yo'))!.successful, isFalse);
+    expect(parser.parse(scan('helloworld')).successful, isTrue);
+    expect(parser.parse(scan('yo')).successful, isFalse);
   });
 
   test('map', () {
     var parser =
         match(new RegExp(r'[A-Za-z]+')).map<int>((r) => r.span!.length);
-    expect(parser.parse(scan('hello'))!.value, 5);
+    expect(parser.parse(scan('hello')).value, 5);
   });
 
   test('negate', () {
     var parser = match('hello').negate(errorMessage: 'world');
-    expect(parser.parse(scan('goodbye world'))!.successful, isTrue);
-    expect(parser.parse(scan('hello world'))!.successful, isFalse);
-    expect(parser.parse(scan('hello world'))!.errors.first.message, 'world');
+    expect(parser.parse(scan('goodbye world')).successful, isTrue);
+    expect(parser.parse(scan('hello world')).successful, isFalse);
+    expect(parser.parse(scan('hello world')).errors.first.message, 'world');
   });
 
   group('opt', () {
@@ -44,13 +44,13 @@ main() {
     var list = match('hel').then(match('lo')).opt();
 
     test('succeeds if present', () {
-      expect(single.parse(scan('hello'))!.successful, isTrue);
-      expect(list.parse(scan('hello'))!.successful, isTrue);
+      expect(single.parse(scan('hello')).successful, isTrue);
+      expect(list.parse(scan('hello')).successful, isTrue);
     });
 
     test('succeeds if not present', () {
-      expect(single.parse(scan('goodbye'))!.successful, isTrue);
-      expect(list.parse(scan('goodbye'))!.successful, isTrue);
+      expect(single.parse(scan('goodbye')).successful, isTrue);
+      expect(list.parse(scan('goodbye')).successful, isTrue);
     });
 
     test('backtracks if not present', () {
diff --git a/packages/combinator/test/value_test.dart b/packages/combinator/test/value_test.dart
index 97ab3543..c987d10f 100644
--- a/packages/combinator/test/value_test.dart
+++ b/packages/combinator/test/value_test.dart
@@ -6,10 +6,10 @@ main() {
   var parser = match('hello').value((r) => 'world');
 
   test('sets value', () {
-    expect(parser.parse(scan('hello world'))!.value, 'world');
+    expect(parser.parse(scan('hello world')).value, 'world');
   });
 
   test('no value if no match', () {
-    expect(parser.parse(scan('goodbye world'))!.value, isNull);
+    expect(parser.parse(scan('goodbye world')).value, isNull);
   });
 }