This is defined on page 93 of the UML 2.5.1 specification under section 7.8.10.6 “Operations” for Namespace. I have reformatted the body with my own indentation and line numbering of the body text for easier understanding (I hope!):

getNamesOfMember(element : NamedElement) : String [0..*]

The query getNamesOfMember() gives a set of all of the names that a member would have in a Namespace,
taking importing into account. In general a member can have multiple names in a Namespace if it is imported
more than once with different aliases.

body:
 1 | if self.ownedMember ->includes(element)
 2 | then Set{element.name}
 3 | else
 4 |   let elementImports : Set(ElementImport)
 5 |      = self.elementImport->select(ei | ei.importedElement = element)
 6 |        in
 7 |        if elementImports->notEmpty() -- <== ???
 8 |        then
 9 |          elementImports->collect(el | el.getName())
10 |          ->asSet()
11 |        else
12 |          self.packageImport->select(
13 |             pi | pi.importedPackage.visibleMembers().oclAsType(NamedElement)
14 |              ->includes(element))
15 |                -> collect(pi | pi.importedPackage.getNamesOfMember(element))
16 |                   ->asSet()
17 |        endif
18 | endif

It seems to me that if the Namespace has any ElementImports, none of the elements originating from any PackageImports would be included in the output due to the innermost if..then..else section starting at line 7?

As far as I understand, a Namespace can have PackageImports and also ElementImports from a different Package, possibly having name conflicts.

Perhaps there is an extra (or missing) parenthesis somewhere?