Keycloak-admin get groups of given user

1

I wanna get groups of given user.
I have try with Java admin SDK, but it return null:

        var serverUrl = "http://localhost:8080";
        var realm = "<real>";
        var clientId = "<client_id>";
        var clientSecret = "<client_secret>";
        var keycloak = KeycloakBuilder.builder()
            .serverUrl(serverUrl)
            .realm(realm)
            .grantType(OAuth2Constants.CLIENT_CREDENTIALS)
            .clientId(clientId)
            .clientSecret(clientSecret)
            .build();

        var realmResource = keycloak.realm(realm);
        var userResource = realmResource.users();
        var user = userResource.searchByEmail("<email>", true).get(0);
        var groups = user.getGroups(); // => null

I search in the API docs and found that there is an API GET /{realm}/users/{id}/groups but don’t found the corresponding API in Keycloak SDK

https://www.keycloak.org/docs-api/20.0.2/rest-api/index.html#_groupmembership