Prepare mockito for null safety:

Change [_findAfter] to throw instead of return null, in the case that a match could not be found. The way the code is before, where `firstWhere` can return null via `orElse`, the type of list is inferred to be a list of nullable elements. The migration tool feeds this nullability up very high. Removing the `orElse` and catching the possible StateError is safer.

* Add /*late*/ hints for the migration tool.

PiperOrigin-RevId: 317387499

example/iss/iss.dart

@@ -22,7 +22,7 @@ import 'package:http/http.dart';
 class IssLocator {
   final Client client;
 
-  Point<double> _position;
+  /*late*/ Point<double> _position;
   Future _ongoingRequest;
 
   IssLocator(this.client);

lib/src/mock.dart

@@ -658,9 +658,8 @@ class _VerifyCall {
   }
 
   RealCall _findAfter(DateTime dt) {
-    return matchingInvocations.firstWhere(
-        (inv) => !inv.verified && inv.timeStamp.isAfter(dt),
-        orElse: () => null);
+    return matchingInvocations
+        .firstWhere((inv) => !inv.verified && inv.timeStamp.isAfter(dt));
   }
 
   void _checkWith(bool never) {
@@ -1001,11 +1000,11 @@ _InOrderVerification get verifyInOrder {
     _verifyCalls.clear();
     var matchedCalls = <RealCall>[];
     for (var verifyCall in tmpVerifyCalls) {
-      var matched = verifyCall._findAfter(dt);
-      if (matched != null) {
+      try {
+        var matched = verifyCall._findAfter(dt);
         matchedCalls.add(matched);
         dt = matched.timeStamp;
-      } else {
+      } on StateError {
         var mocks = tmpVerifyCalls.map((vc) => vc.mock).toSet();
         var allInvocations =
             mocks.expand((m) => m._realCalls).toList(growable: false);

test/invocation_matcher_test.dart

@@ -153,7 +153,7 @@ abstract class Interface {
 ///
 /// Any call always returns an [Invocation].
 class Stub implements Interface {
-  static Invocation lastInvocation;
+  static /*late*/ Invocation lastInvocation;
 
   const Stub();