wip eh, treat missing as empty

Author: gnprice

lib/model/push_device.dart

@@ -13,7 +13,7 @@ import 'store.dart';
 class PushDeviceManager extends PerAccountStoreBase {
   PushDeviceManager({
     required super.core,
-    required Map<int, PushDeviceEntry>? pushDevices,
+    required Map<int, PushDeviceEntry> pushDevices,
   }) : _registrant = PushTokenRegistrant(core: core),
        _pushDevices = pushDevices;
 
@@ -44,19 +44,13 @@ class PushDeviceManager extends PerAccountStoreBase {
   /// For docs, search for "push_device"
   /// in <https://zulip.com/api/register-queue>.
   ///
-  /// Null if the server was old and did not provide such a map.
-  // TODO(server-11) make non-nullable when [InitialSnapshot.pushDevices] is
-  late Map<int, PushDeviceEntry>? pushDevices =
-    _pushDevices == null ? null : UnmodifiableMapView(_pushDevices);
-  final Map<int, PushDeviceEntry>? _pushDevices;
+  /// An absent map in [InitialSnapshot] (from an old server) is treated
+  /// as empty, since a server without this feature has none of these records.
+  // TODO(server-11) simplify doc re an absent map
+  late Map<int, PushDeviceEntry> pushDevices = UnmodifiableMapView(_pushDevices);
+  final Map<int, PushDeviceEntry> _pushDevices;
 
   void handlePushDeviceEvent(PushDeviceEvent event) {
-    if (_pushDevices == null) {
-      // TODO(log)... but in principle this is possible if the server was
-      //   upgraded, gaining support for this feature,
-      //   in the life of the event queue.
-      return;
-    }
     final pushAccountId = int.tryParse(event.pushAccountId, radix: 10);
     if (pushAccountId == null) return; // TODO(log); TODO(#1764) push this to API parser
     _pushDevices[pushAccountId] = event.data;

lib/model/store.dart

@@ -530,7 +530,7 @@ class PerAccountStore extends PerAccountStoreBase with
         allRealmEmoji: initialSnapshot.realmEmoji),
       userSettings: initialSnapshot.userSettings,
       pushDevices: PushDeviceManager(core: core,
-        pushDevices: initialSnapshot.pushDevices),
+        pushDevices: initialSnapshot.pushDevices ?? {}),
       savedSnippets: SavedSnippetStoreImpl(core: core,
         savedSnippets: initialSnapshot.savedSnippets ?? []),
       typingNotifier: TypingNotifier(realm: realm),