Should Validation occurs for unselected value?

Question

I have a JSF page as follows :
<h:selectOneListBox ... value="#{Bean.selectedOption}" ...>
<f:selectItem itemValue="Ans01" itemLabel="Ford" />
<f:selectItem itemValue="Ans02" itemLabel="Honda" />
</h:selectOneListBox>
<h:commandButton ...value="submit" action="nextPage" />
The Bean has the following method:
private String selectedOption;
public String getSelectedOption() {
// selectedOption = null; works - list with no pre-selection on list
// selectedOption = "Ans01"; works - list with "Ford" pre-selected on list
selectedOption = ""; fails during UPDATE_MODEL phase with
return selectedOption;
When the page is displayed, no selection is made on the selectItems list and the submit button is triggered. A JSF Validation Error occurs .
selectedOption initially has invalid value, and JSF does not preselect any list item. User does not select anything from the list, so there is no input , why does Validation triggered in this case ?
Is there any attribute in the control that I could specify to skip validation if there is no user interaction with the control ?
Thanks for any suggestion.
Alex.

Answer 1

What is the problem with the null value as you mentioned in comments that it works....
It you intialize the list with a value that does not exist like "", in the validation phase, the system will check that this value belongs to the available value and as it is not the case, a validation error occurs. The empty string is not equal to the null value...