If you want to force it to be a scalar, you can use the scalar keyword instead of a throwaway variable:

$ perl -MData::Printer -E 'sub some_sub { return 1 } ; %h = ( foo => s
+ome_sub(), bar => 42 ); p %h'
{
    bar   42,
    foo   1
}

$ perl -MData::Printer -E 'sub some_sub { return } ; %h = ( foo => som
+e_sub(), bar => 42 ); p %h'
{
    42    undef,
    foo   "bar"
}

$ perl -MData::Printer -E 'sub some_sub { return } ; %h = ( foo => sca
+lar some_sub(), bar => 42 ); p %h'
{
    bar   42,
    foo   undef
}
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