Validators not invoked for empty selectManyCheckbox components

Custom validators are not invoked for selectManyCheckbox component, if the component has no selections made; this can be an issue if we want to handle the null/empty case in a validator. The following context params address this case:

<context-param>
<param-name>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</param-name>
<param-value>true</param-value>
</context-param>

<context-param>
<param-name>javax.faces.VALIDATE_EMPTY_FIELDS</param-name>
<param-value>true</param-value>
</context-param>

But these params do not affect the behavior here. Based on my understanding of the spec, it seems that this behavior should be changed.