XPath to return default value if node not present

In XPath 1.0, use:

concat(/Foo/Baz,
       substring('not-found', 1 div not(/Foo/Baz)))

If you want to handle the posible empty Baz element, use:

concat(/Foo/Baz,
       substring('not-found', 1 div not(/Foo/Baz[node()])))

With this input:

<Foo>
    <Baz/>
</Foo>

Result: not-found string data type.

Special case: If you want to get 0 if numeric node is missing or empty, use sum(/Foo/Baz) function

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