XQTS - Test externalcontextitem-1.xq, nodename selection on an undefined context same as on empty sequence

The test externalcontextitem-1.xq performs a nodename selection with no context item. The reference result is the error XPDY0002. 
I couldn't find a clear answer in the spec why  a node selection on an empty sequence (which implies no context item) return the empty seq. and the node selection with no context item returns an error. 
It's clear why functions that try to access the context item, report an error when there is no context item, however not when a nodename selection is performed. 
Regards Margaret
... Margaret A. Grün-Kerr
... Quality Assurance Engineer
... Altova GmbH

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