def missing_hash_entries_as_string(the_hash, *keys)
    if keys.size == 1 && keys.first.is_a?(Array)
      keys = keys.first
    end
    missing_keys = missing_hash_entries(the_hash, *keys)
    missing_keys.empty? ? nil : missing_keys.inspect
  end
def missing_hash_entries_as_string(the_hash, *keys)
    if keys.size == 1 && keys.first.is_a?(Array)
      keys = keys.first
    end
    missing_keys = missing_hash_entries(the_hash, *keys)
    missing_keys.empty? ? nil : missing_keys.inspect
  end
Looks to see which keys, if any, are missing from the hash.
 @return nil if none missing, else comma separated string of missing keys.