#fixed code
                                public void verifyAccess(AccessToken token, RealmModel realm, ClientModel client, UserModel user) throws OAuthErrorException {
        ApplicationModel clientApp = (client instanceof ApplicationModel) ? (ApplicationModel)client : null;


        if (token.getRealmAccess() != null) {
            for (String roleName : token.getRealmAccess().getRoles()) {
                RoleModel role = realm.getRole(roleName);
                if (role == null) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_GRANT, "Invalid realm role " + roleName);
                }
                if (!user.hasRole(role)) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "User no long has permission for realm role: " + roleName);
                }
                if (!client.hasScope(role)) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Client no longer has realm scope: " + roleName);
                }
            }
        }
        if (token.getResourceAccess() != null) {
            for (Map.Entry<String, AccessToken.Access> entry : token.getResourceAccess().entrySet()) {
                ApplicationModel app = realm.getApplicationByName(entry.getKey());
                if (app == null) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Application no longer exists", "Application no longer exists: " + entry.getKey());
                }
                for (String roleName : entry.getValue().getRoles()) {
                    RoleModel role = app.getRole(roleName);
                    if (role == null) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_GRANT, "Invalid refresh token", "Unknown application role: " + roleName);
                    }
                    if (!user.hasRole(role)) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "User no long has permission for application role " + roleName);
                    }
                    if (clientApp != null && !clientApp.equals(app) && !client.hasScope(role)) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Client no longer has application scope" + roleName);
                    }
                }
            }
        }
    }
#vulnerable code 
                                public void verifyAccess(AccessToken token, RealmModel realm, ClientModel client, UserModel user) throws OAuthErrorException {
        ApplicationModel clientApp = (client instanceof ApplicationModel) ? (ApplicationModel)client : null;


        if (token.getRealmAccess() != null) {
            for (String roleName : token.getRealmAccess().getRoles()) {
                RoleModel role = realm.getRole(roleName);
                if (role == null) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_GRANT, "Invalid realm role " + roleName);
                }
                if (!user.hasRole(role)) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "User no long has permission for realm role: " + roleName);
                }
                if (!client.hasScope(role)) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Client no longer has realm scope: " + roleName);
                }
            }
        }
        if (token.getResourceAccess() != null) {
            for (Map.Entry<String, AccessToken.Access> entry : token.getResourceAccess().entrySet()) {
                ApplicationModel app = realm.getApplicationByName(entry.getKey());
                if (app == null) {
                    throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Application no longer exists", "Application no longer exists: " + app.getName());
                }
                for (String roleName : entry.getValue().getRoles()) {
                    RoleModel role = app.getRole(roleName);
                    if (role == null) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_GRANT, "Invalid refresh token", "Unknown application role: " + roleName);
                    }
                    if (!user.hasRole(role)) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "User no long has permission for application role " + roleName);
                    }
                    if (clientApp != null && !clientApp.equals(app) && !client.hasScope(role)) {
                        throw new OAuthErrorException(OAuthErrorException.INVALID_SCOPE, "Client no longer has application scope" + roleName);
                    }
                }

            }
        }
    } 
                            #location 23 
                            #vulnerability type NULL_DEREFERENCE