Looking through perlop I found an example showing one nastiness:

  @info = stat($file) || die;   # oops, scalar sense of stat!
  @info = stat($file) or die;   # better, now @info gets its due
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I guess an equivalent to your situation might be:

  my @Candidates = @_ or return;
  my @Candidates = @_ || return;
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The second will return undef or set the only element of @Candidates to the number of arguments passed in.   So in effect 'or' is allowing operators, including assignments, to be completely evaluated, without inducing any side-effects.