How to set vaadin combobox value with beanitemcontainer?

Hi friends,

I am trying to set combobox value for update a bean item in vaadin. But the combobox selected value comes null when I open it. How can i bind value?

my Company bean;

private int companyID;
private String companyName;
private String email;
private String phone;
private String location;
private Date creationDate;
private Date expireDate;
private boolean inActive;

my User Bean;

private int userId;
private String username;
private String password;
private Company company;
private EUserRole userRole; 
private String email;
private String firstName;
private String lastName;

ui class;

BeanItemContainer<Company> itemContainer = new BeanItemContainer<Company>(Company.class); 
itemContainer.addAll(companyService.getAllCompanies());
cbxCompanyName = new ComboBox("Company Name", itemContainer);
cbxCompanyName.setWidth("50%");
cbxCompanyName.setNullSelectionAllowed(false);
cbxCompanyName.setItemCaptionMode(ItemCaptionMode.PROPERTY);
cbxCompanyName.setImmediate(true);
cbxCompanyName.setItemCaptionPropertyId("companyName");
cbxCompanyName.setNewItemsAllowed(false);
details.addComponent(cbxCompanyName);

cbxCompanyName.setValue(admin.getCompany());

here is my  secreenshot;