Android Drive NPE upload file

I'm trying to send the database file to Google Drive, I imported the librerire necessary, but when I try to upload the file to GoogleDrive I get NPE.

public class Main extends BaseDemoActivity {
private Drive service;

@Override
public void onConnected(Bundle connectionHint) {
    super.onConnected(connectionHint);
    // create new contents resource
    com.google.android.gms.drive.Drive.DriveApi.newDriveContents(getGoogleApiClient())
            .setResultCallback(driveContentsCallback);
}

final private ResultCallback<DriveContentsResult> driveContentsCallback = new
        ResultCallback<DriveContentsResult>() {
            @Override
            public void onResult(final DriveContentsResult result) {
                if (!result.getStatus().isSuccess()) {
                    showMessage("Error while trying to create new file contents");
                    return;
                }

                new Thread() {
                    @Override
                    public void run() {
                         try {
                            java.io.File externalDB = new java.io.File(Environment.getExternalStorageDirectory(), getString(R.string.app_name) + "/data.crypt");
                            java.io.File fileContent = new java.io.File(externalDB.getPath());
                            FileContent mediaContent = new FileContent("application/x-sqlite3", fileContent);

                            com.google.api.services.drive.model.File body =
                                    new com.google.api.services.drive.model.File();
                            body.setTitle("data.crypt");
                            body.setMimeType("application/x-sqlite3");
                            com.google.api.services.drive.model.File file =
                                    service.files().insert(body, mediaContent).execute();
                            if (file != null) {
                                Log.d("GoogleDrive", "File Uploaded");
                            }

                        } catch (UserRecoverableAuthIOException e) {
                            //startActivityForResult(e.getIntent(), REQUEST_AUTHORISATION);
                        } catch (IOException e) {
                            e.printStackTrace();
                        }

                    }
                }
                        .start();
            }

        };
...
...

The line of NPE com.google.api.services.drive.model.File file = service.files().insert(body, mediaContent).execute();

Log

    01-17 11:48:32.387 11372-12201/? E/AndroidRuntime: FATAL EXCEPTION: Thread-34061
01-17 11:48:32.387 11372-12201/? E/AndroidRuntime: Process: chris.con, PID: 11372
01-17 11:48:32.387 11372-12201/? E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.api.services.drive.Drive$Files com.google.api.services.drive.Drive.files()' on a null object reference
01-17 11:48:32.387 11372-12201/? E/AndroidRuntime:     at chris.con.Main$1$1.run(Main.java:51)