Minor Description
I believe that the documentation on AbstractSelectSingleChoice regarding nullValid is misleading. This documentation appears in isNullValid()
and setNullValid(). I think the following is more accurate and informative:
Determines whether or not the null value should be included in the
list of choices when the field's model value is nonnull, and whether or
not the null_valid string property (e.g. "Choose One") should be
displayed until a nonnull value is selected.
If set to false, then "Choose One" will be displayed when the value is
null. After a value is selected, and that change is propagated to the
underlying model, the user will no longer see the "Choose One" option,
and there will be no way to reselect null as the value.
If set to true, the null string property (the empty string, by default)
will always be displayed as an option, whether or not a nonnull value
has ever been selected.
Note that this setting has no effect on validation; in order to guarantee
that a value will be specified on form validation, call setRequired(true). This is because even if setNullValid() is called with false, the user can fail to provide a value simply by never activating (i.e. clicking on) the component.
For the nullValid data member, I suggest this comment:
"whether or not null will be offered as a choice once a nonnull value is saved"
