%hash = (
  A => 'that',
  B => 'those',
  C => 'groovy',
  D => 'artichoke',
  E => undef,
  F => 'flipping',
);

@check = qw( A D F );  # change to 'E' or 'Z' to see

if (@check == grep defined, @hash{@check}) {
  # ok
}