Changed id to be optional on [EventModel], [TaskModel] and [UserModel]

lib/src/resources/firestore_provider.dart

@@ -40,71 +40,13 @@ class FirestoreProvider {
         );
       },
     );
+
     return Observable(mappedStream);
   }
 
   //-------------------------Task related operations----------------------------
 
-  /// Adds a task to firestore.
+  /// Returns a stream of [List<Task>]
-  Future<void> addTask(TaskModel task) async {
-    try {
-      final dataMap = task.toFirestoreMap();
-      await firestore.collection('tasks').add(dataMap);
-    } catch (e) {
-      print('Error adding task to firestore: $e');
-    }
-  }
-
-  /// Returns a Stream of a single task from an id.
-  Observable<TaskModel> getTask(String id) {
-    final mappedStream =
-        firestore.collection('tasks').document(id).snapshots().map(
-      (DocumentSnapshot snapshot) {
-        return TaskModel.fromFirestore(
-          snapshot.data,
-          id: snapshot.documentID,
-        );
-      },
-    );
-
-    return Observable(mappedStream);
-  }
-
-  /// Deletes a task from firestore.
-  Future<void> deleteTask(String id) async {
-    try {
-      final documentReference = firestore.collection('tasks').document(id);
-      await documentReference.delete();
-    } catch (e) {
-      print('Error deleting task from firestore: $e');
-    }
-  }
-
-  /// Updates a task in firestore.
-  ///
-  /// Only the [text], [priority] and [done] attributes can be update.
-  /// Provide at least one of these values.
-  Future<void> updateTask(
-    String id, {
-    String text,
-    int priority,
-    bool done,
-  }) async {
-    final newData = <String, dynamic>{
-      'text': text,
-      'priority': priority,
-      'done': done,
-    };
-    newData.removeWhere((key, value) => value == null);
-    try {
-      final documentReference = firestore.collection('tasks').document(id);
-      await documentReference.setData(newData, merge: true);
-    } catch (e) {
-      print('Error updating task in firestore: $e');
-    }
-  }
-
-  /// Returns a stream of [List<Task>] that correspond to a particular user.
   ///
   /// The [event] parameter is used to query tasks that are part of a certain
   /// event.
@@ -134,9 +76,23 @@ class FirestoreProvider {
     return Observable(mappedStream);
   }
 
+  Observable<TaskModel> getTask(String id) {
+    final mappedStream =
+        firestore.collection('tasks').document(id).snapshots().map(
+      (DocumentSnapshot snapshot) {
+        return TaskModel.fromFirestore(
+          snapshot.data,
+          id: snapshot.documentID,
+        );
+      },
+    );
+
+    return Observable(mappedStream);
+  }
+
   //-----------------------Event related operations-----------------------------
 
-  // TODO: Change the Events collction name to 'events' in forestore.
+  // TODO: Change the Events collction name to 'events'
   Observable<List<EventModel>> getUserEvents(String userDocumentId) {
     final mappedStream = firestore
         .collection('users')