NoSuchMethodError: The method '[]' was called on null. Receiver: null Tried Calling: []("firstName")

I am getting this error in my flutter app that uses firebase firestore as backend

This is my stacktrace:

E/flutter (13517): [ERROR:flutter/shell/common/shell.cc(93)] Dart Unhandled Exception: NoSuchMethodError: The getter 'id' was called on null.
E/flutter (13517): Receiver: null
E/flutter (13517): Tried calling: id, stack trace: #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:38:5)
E/flutter (13517): #1      EnterpriseFirebaseApi.fetchEnterprisesByUser (package:paprika_app/authentication/services/enterprise_services.dart:22:42)
E/flutter (13517): #2      AuthenticationRepository.fetchEnterprisesByUser (package:paprika_app/authentication/resources/authentication_repository.dart:33:30)
E/flutter (13517): #3      AuthenticationBloc._fetchEnterprisesByUser (package:paprika_app/authentication/blocs/authentication_bloc.dart:143:10)
E/flutter (13517): #4      AuthenticationBloc.userLogged.<anonymous closure> (package:paprika_app/authentication/blocs/authentication_bloc.dart:103:15)
E/flutter (13517): <asynchronous suspension>
E/flutter (13517): #5      AuthenticationBloc.userLogged (package:paprika_app/authentication/blocs/authentication_bloc.dart:99:5)
E/flutter (13517): <asynchronous suspension>

This is E/flutter (13517): #1 EnterpriseFirebaseApi.fetchEnterprisesByUser (package:paprika_app/authentication/services/enterprise_services.dart:22:42)

/// Looking for enterprises with this user
    await FirebaseFirestore.instance
        .collection('enterprises_users')
        .where('userId', isEqualTo: user.id)
        .where('state', isEqualTo: 'A')
        .get()
        .then((docs) {
      docSnapshotList.addAll(docs.docs);
    });

can anyone help me with this...