I think there's some updates needed for the packages as well.
Error code as below:
posix-4.1.0/lib/src/pwd.dart:322:35: Error: Field 'name' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? name;
^
posix-4.1.0/lib/src/pwd.dart:326:35: Error: Field 'password' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? password;
^
posix-4.1.0/lib/src/pwd.dart:330:17: Error: Field 'uid' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external int? uid;
^
posix-4.1.0/lib/src/pwd.dart:334:17: Error: Field 'gid' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external int? gid;
^
posix-4.1.0/lib/src/pwd.dart:337:35: Error: Field 'gecos' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? gecos;
^
posix-4.1.0/lib/src/pwd.dart:340:35: Error: Field 'dir' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? dir;
^
posix-4.1.0/lib/src/pwd.dart:343:35: Error: Field 'shell' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? shell;
^
posix-4.1.0/lib/src/grp.dart:369:35: Error: Field 'name' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? name;
^
posix-4.1.0/lib/src/grp.dart:372:35: Error: Field 'passwd' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? passwd;
^
posix-4.1.0/lib/src/grp.dart:376:17: Error: Field 'gid' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external int? gid;
^
posix-4.1.0/lib/src/grp.dart:379:48: Error: Field 'mem' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Pointer<ffi.Int8>>? mem;
^
posix-4.1.0/lib/src/string/string.dart:830:38: Error: Field '_unique___locales_item_0' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_0;
^
posix-4.1.0/lib/src/string/string.dart:832:38: Error: Field '_unique___locales_item_1' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_1;
^
posix-4.1.0/lib/src/string/string.dart:834:38: Error: Field '_unique___locales_item_2' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_2;
^
posix-4.1.0/lib/src/string/string.dart:836:38: Error: Field '_unique___locales_item_3' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_3;
^
posix-4.1.0/lib/src/string/string.dart:838:38: Error: Field '_unique___locales_item_4' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_4;
^
posix-4.1.0/lib/src/string/string.dart:840:38: Error: Field '_unique___locales_item_5' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_5;
^
posix-4.1.0/lib/src/string/string.dart:842:38: Error: Field '_unique___locales_item_6' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_6;
^
posix-4.1.0/lib/src/string/string.dart:844:38: Error: Field '_unique___locales_item_7' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_7;
^
posix-4.1.0/lib/src/string/string.dart:846:38: Error: Field '_unique___locales_item_8' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_8;
^
posix-4.1.0/lib/src/string/string.dart:848:38: Error: Field '_unique___locales_item_9' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_9;
^
posix-4.1.0/lib/src/string/string.dart:850:38: Error: Field '_unique___locales_item_10' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_10;
^
posix-4.1.0/lib/src/string/string.dart:852:38: Error: Field '_unique___locales_item_11' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_11;
^
posix-4.1.0/lib/src/string/string.dart:854:38: Error: Field '_unique___locales_item_12' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<locale_data>? _unique___locales_item_12;
^
posix-4.1.0/lib/src/string/string.dart:861:35: Error: Field '_unique___names_item_0' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_0;
^
posix-4.1.0/lib/src/string/string.dart:863:35: Error: Field '_unique___names_item_1' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_1;
^
posix-4.1.0/lib/src/string/string.dart:865:35: Error: Field '_unique___names_item_2' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_2;
^
posix-4.1.0/lib/src/string/string.dart:867:35: Error: Field '_unique___names_item_3' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_3;
^
posix-4.1.0/lib/src/string/string.dart:869:35: Error: Field '_unique___names_item_4' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_4;
^
posix-4.1.0/lib/src/string/string.dart:871:35: Error: Field '_unique___names_item_5' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_5;
^
posix-4.1.0/lib/src/string/string.dart:873:35: Error: Field '_unique___names_item_6' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_6;
^
posix-4.1.0/lib/src/string/string.dart:875:35: Error: Field '_unique___names_item_7' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_7;
^
posix-4.1.0/lib/src/string/string.dart:877:35: Error: Field '_unique___names_item_8' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_8;
^
posix-4.1.0/lib/src/string/string.dart:879:35: Error: Field '_unique___names_item_9' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_9;
^
posix-4.1.0/lib/src/string/string.dart:881:35: Error: Field '_unique___names_item_10' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_10;
^
posix-4.1.0/lib/src/string/string.dart:883:35: Error: Field '_unique___names_item_11' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_11;
^
posix-4.1.0/lib/src/string/string.dart:885:35: Error: Field '_unique___names_item_12' cannot be nullable or have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct` or `Union`.
external ffi.Pointer<ffi.Int8>? _unique___names_item_12;
I think there's some updates needed for the packages as well.
Error code as below: