XPath to return default value if node not present -

say have pair of xml documents

<foo>     <bar/>     <baz>mystring</baz> </foo>

and

<foo>     <bar/> </foo>

i want xpath (version 1.0 only) returns "mystring" first document , "not-found" second. tried

(string('not-found') | //baz)[last()]

but left hand side of union isn't node-set

in xpath 1.0, use:

concat(/foo/baz,        substring('not-found', 1 div not(/foo/baz)))

if want handle posible empty baz element, use:

concat(/foo/baz,        substring('not-found', 1 div not(/foo/baz[node()])))

with input:

<foo>     <baz/> </foo>

result: not-found string data type.

TY