fix errors

lib/pages/customer/model/customer_model.dart

@@ -96,6 +96,25 @@ class CustomerModel extends BaseModel {
     return User.fromMap(snap.data, snap.documentID);
   }
 
+  Future<List<User>> getInvoiceUsers(String fcsShipmentID) async {
+    List<User> users = [];
+    try {
+      var snaps = await Firestore.instance
+          .collection(
+              "/$fcs_shipment_collection/$fcsShipmentID/$user_collection")
+          .where("pending_invoice_carton_count", isGreaterThan: 0)
+          .getDocuments(source: Source.server);
+      users = snaps.documents.map((documentSnapshot) {
+        var user =
+            User.fromMap(documentSnapshot.data, documentSnapshot.documentID);
+        return user;
+      }).toList();
+    } catch (e) {
+      log.warning("Error!! $e");
+    }
+    return users;
+  }
+
   Future<void> enableUser(User user, bool enabled) {
     return Services.instance.userService.enableUser(user.id, enabled);
   }