Issues in Permission handler in building apk

[pratikraman-dev]

Compiler message:
lib/services/contacts.dart:9:41: Error: Method not found: 'PermissionHandler'.
PermissionStatus permission = await PermissionHandler()
^^^^^^^^^^^^^^^^^
lib/services/contacts.dart:10:32: Error: Getter not found: 'PermissionGroup'.
.checkPermissionStatus(PermissionGroup.contacts);
^^^^^^^^^^^^^^^
lib/services/contacts.dart:11:32: Error: Method not found: 'PermissionHandler'.
bool showRationale = await PermissionHandler()
^^^^^^^^^^^^^^^^^
lib/services/contacts.dart:12:51: Error: Getter not found: 'PermissionGroup'.
.shouldShowRequestPermissionRationale(PermissionGroup.contacts) &&
^^^^^^^^^^^^^^^
lib/services/contacts.dart:14:40: Error: Getter not found: 'unknown'.
if (permission == PermissionStatus.unknown || showRationale) {
^^^^^^^
lib/services/contacts.dart:16:11: Error: 'PermissionGroup' isn't a type.
Map<PermissionGroup, PermissionStatus> statuses =
^^^^^^^^^^^^^^^
lib/services/contacts.dart:17:17: Error: Method not found: 'PermissionHandler'.
await PermissionHandler()
^^^^^^^^^^^^^^^^^
lib/services/contacts.dart:18:36: Error: Getter not found: 'PermissionGroup'.
.requestPermissions([PermissionGroup.contacts]);
^^^^^^^^^^^^^^^
lib/services/contacts.dart:20:23: Error: Getter not found: 'PermissionGroup'.
return statuses[PermissionGroup.contacts];
^^^^^^^^^^^^^^^
Target kernel_snapshot failed: Exception: Errors during snapshot creation: null
build failed.

FAILURE: Build failed with an exception.