f:validator tag validatorId attribute doesn't resolve EL Expressions?

Question

I have a set of custom validators that I've written to validate certain data types used in our application. I have tested all of them and verified that they all work. Now I want to display a data table showing a list of data input fields, each bound to an object of a different type. During the iteration the 'item' has a method called "getValidatorIdentifier()" which returns a String that is the ID of the validator registered in my faces_config.xml file. Using the following code, I want to set the validatorId dynamically for each inputText field in my data table.
<h:dataTable var="item" ..... >
<h:inputText id="itemValue"
required="#{item.required}"
value="#{item.relatedAsset.asset}">
<f:validator validatorId="#{item.validatorIdentifier}" /> <!-- PROBLEM?-->
</h:inputText>
</h:dataTable>
Now, when I hard-code the validatorId attribute to the registered validator ID, it works fine. When I try to use the EL expression, as in the above code, I get the following when I access the page:
java.lang.NullPointerException: Argument Error: One or more parameters are null.
     com.sun.faces.application.ApplicationImpl.createValidator(ApplicationImpl.java:712)
     javax.faces.webapp.ValidatorTag.createValidator(ValidatorTag.java:146)
     javax.faces.webapp.ValidatorTag.doStartTag(ValidatorTag.java:109)
I looked in the O'Reilly JavaServer Faces book and it states that the validatorId attribute should accept an EL expression type of 'any', so I am assuming that the expression #{item.validatorIdentifier} should work.
Am I making a mistake here, or is there a bug I don't know about in the f:validator tag?
Thanks for your help.

Answer 1

A little more information on this issue.
When I attempt to resolve the validatorId from the 'item' var (the variable in the data table iteration) I get the problem described in my first posting. Now if I create an outputText element simply to echo the value of item.validatorIdentifier, it displays the correct value that I would expect.
<f:validator validatorId="#{item.validatorIdentifier}" /> <!-- This fails with the error already described-->
<h:outputText value="#{item.validatorIdentifier}"/> <!-- this works just fine -->
Now, just to see if it was the EL, I modified the validator tag to use an EL expression bound to a getValidatorId() method in a managed bean class. In other words, when I'm NOT trying to resolve the validatorId from the iteration variable, an EL expression works.
<f:validator validatorId="#{myManagedBean.validatorId}" /> <!-- This works just fine-->
But, this is not a solution, since each element in my dataTable iteration needs to report to me what its validator ID should be.