making obersver query predicate nullable

Author: kvs-coder

example/lib/main.dart

@@ -492,7 +492,7 @@ class _MyAppState extends State<MyApp> {
   }
 
   void observerQuery(List<String> identifiers) async {
-    final sub = HealthKitReporter.observerQuery(identifiers, _predicate,
+    final sub = HealthKitReporter.observerQuery(identifiers, null,
         onUpdate: (identifier) async {
       print('Updates for observerQuerySub - $identifier');
       print(identifier);

ios/Classes/ObserverQueryStreamHandler.swift

@@ -21,16 +21,19 @@ public final class ObserverQueryStreamHandler: NSObject {
 extension ObserverQueryStreamHandler: StreamHandlerProtocol {
     public func setQueries(arguments: [String: Any], events: @escaping FlutterEventSink) throws {
         guard
-            let identifiers = arguments["identifiers"] as? [String],
-            let startTimestamp = arguments["startTimestamp"] as? Double,
-            let endTimestamp = arguments["endTimestamp"] as? Double
+            let identifiers = arguments["identifiers"] as? [String]
         else {
             return
         }
-        let predicate = NSPredicate.samplesPredicate(
-            startDate: Date.make(from: startTimestamp),
-            endDate: Date.make(from: endTimestamp)
-        )
+        var predicate: NSPredicate?
+        if
+            let startTimestamp = arguments["startTimestamp"] as? Double,
+            let endTimestamp = arguments["endTimestamp"] as? Double {
+            predicate = NSPredicate.samplesPredicate(
+                startDate: Date.make(from: startTimestamp),
+                endDate: Date.make(from: endTimestamp)
+            )
+        }
         for identifier in identifiers {
             guard let type = identifier.objectType as? SampleType else {
                 return

lib/health_kit_reporter.dart

@@ -164,12 +164,14 @@ class HealthKitReporter {
   /// Provide the [predicate] to set the date interval.
   ///
   static StreamSubscription<dynamic> observerQuery(
-      List<String> identifiers, Predicate predicate,
+      List<String> identifiers, Predicate? predicate,
       {required Function(String) onUpdate}) {
     final arguments = <String, dynamic>{
       'identifiers': identifiers,
     };
-    arguments.addAll(predicate.map);
+    if (predicate != null) {
+      arguments.addAll(predicate.map);
+    }
     return _observerQueryChannel
         .receiveBroadcastStream(arguments)
         .listen((event) {