Omnifaces Validateorder Disabling

I'm trying to use validateOrder component to validate two java.util.Date objects. It is similar to showcase example on this link (PrimeFaces example). Everything works perfect, but

Solution 1:

Let the disabled attribute check if the 2nd field is filled in. If it's not filled in, the request parameter value associated with field's client ID will be empty. Use exaclty that to let disabled attribute evaluate to true.

<p:calendar...binding="#{endDate}" />
...
<o:validateOrder...disabled="#{empty param[endDate.clientId]}" />

Code is as-is. No additional backing bean property necessary for binding.

See also:

• How does the 'binding' attribute work in JSF? When and how should it be used?