The empty sequence and xs:boolean

Given that:

<xsl:variable name="v1" select="/nothing eq 'a' " as="xs:boolean"/>

will cause an exception if /nothing returns (), what is best / most
efficient way to construct this variable?

<xsl:variable name="v1" select="/nothing = 'a' " as="xs:boolean"/>

or

<xsl:variable name="v1" select="boolean(/nothing eq 'a')" as="xs:boolean"/>

or

something else?



-- 
Andrew Welch
http://andrewjwelch.com