How to tell using XPath if an element is present and non empty?

Question

I have an input XML something on this line:

<Holding id="12">
    <Policy>
        <HoldingForm tc="1">Individual</HoldingForm>
        <PolNumber>848433</PolNumber>
        <LineOfBusiness tc="1">Life</LineOfBusiness>
        <CarrierCode>67644</CarrierCode>
    </Policy>
</Holding>

My manipulation on this XML depends on if <PolNumber> (its an optional element in schema) has a value or not. I'm using Mule 3.3 xpath evaluator to do this and my XPath expression looks this:

<expression-filter expression="#[xpath('//acord:Holding/acord:Policy/acord:PolNumber').text != empty]"/> 

This works fine as long as <PolNumber> element is present or <PolNumber/> is empty element. But if <PolNumber> is absent, above expression throws exception.

I tried using XPath boolean function but it returns true for <PolNumber/>. Is there a better way of checking if an element is present and non-empty?

EDIT:

This is the configuration of namespace manager in my mule config

<xm:namespace-manager includeConfigNamespaces="true">
    <xm:namespace prefix="acord" uri="http://ACORD.org/Standards/Life/2" />
    <xm:namespace prefix="soap" uri="http://schemas.xmlsoap.org/soap/encoding/" />
</xm:namespace-manager>

Answer 1

Use:

boolean(//acord:Holding/acord:Policy/acord:PolNumber/text()[1])

this produces true() if //acord:Holding/acord:Policy/acord:PolNumber has a first text-node child, and false() otherwise.

Do note: This is more efficient than counting all text-node children just to compare the count with 0.