Use undef to mean 'BAD' and your sample sub becomes:

sub ConfigRead {
    my %hArgs = @_;
    
    # stick some cool stuff in their variables
}
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Then instead of:

die "horribly" if $hArgs{sFILE} eq 'BAD';
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you can:

die "horribly" if !exists $hArgs{sFILE};
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or:

$hArgs{sFILE} //= 'default.sFile';
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as appropriate.