Open file with an object that stores another object (ArrayList wrapper)

Good, I am having problems to be able to advance with a project, the question is that I have an 'Exhibition' class, which in turn has a 'Works' field that is an ArrayList package. When I save my class Exposure does not jump any type of error, it generates the file to me apparently well (if I add or delete content and I return to save it varies the size of the file). And when I open it again, it seems to open the Exposure class, but when I check the contents of the ArrayList, I verify that it is not loading the data that should be from that file. Here I leave the fragments of the code, a greeting and thanks in advance. (Both the Exposure class and the ArrayList wrapper implement the Serializable

public class Exposicion implements Serializable{
    private Obras museo = Obras.getInstance(); // Fondos del museo.
    ...

Selecting the file from the JFileChooser - >

private void abrirFichero() throws FileNotFoundException,
        ClassNotFoundException, IOException {
    fileChooser.setAcceptAllFileFilterUsed(false);
    fileChooser.addChoosableFileFilter(filtro);
    if (fileChooser.showDialog(fileChooser, "Abrir Fichero") == JFileChooser.APPROVE_OPTION) {
        Fichero.FICHERO = fileChooser.getSelectedFile();
        exposicion = (Exposicion) Fichero.abrir(fileChooser.getSelectedFile());
        frame.setTitle(Fichero.getFichero().getName());
        JOptionPane.showMessageDialog(null, "Cargado con exito");
    ....

Opening the File - >

public static Object abrir(File archivo) throws IOException, ClassNotFoundException {
    try (ObjectInputStream in = new ObjectInputStream(new FileInputStream(archivo))) {
        return in.readObject();
    }
}

EDITO - > I have tried to modify the field Works once I load the file, but in this way it does not load the content in the wrapper:

exposicionAux = (Exposicion) Fichero.abrir(fileChooser.getSelectedFile());
exposicion = exposicionAux;
exposicion.setMuseo(exposicionAux.getMuseo());

SOLVED - >

The error was in the wrapper of ArrayList , because it had declared it static

private static ArrayList<ObraDeArte> obras;

and the static elements can not be serialized.

private ArrayList <ObraDeArte> obras;