I am trying to access one of my vocabularies from Eclipse using Nuxeo SDK.
But I keep getting a nullPointerException when trying to create a session

DirectoryService dirService = DirectoryHelper.getDirectoryService();

DocumentModel entry = null;
Session dirSession = null;
try {
    dirSession = dirService.open(<VOCABULARY_ID>);
} ...

Do I need to configure the nuxeo-sdk.conf to use a postgreSQL database?