def missing_hash_entries(the_hash, *keys)
    # Support passing either an Array or multiple args:
    if keys.size == 1 && keys.first.is_a?(Array)
      keys = keys.first
    end

    keys - the_hash.keys
  end
def missing_hash_entries(the_hash, *keys)
    # Support passing either an Array or multiple args:
    if keys.size == 1 && keys.first.is_a?(Array)
      keys = keys.first
    end

    keys - the_hash.keys
  end
Looks to see which keys, if any, are missing from the hash.
 @return an array of missing keys (empty if none)