Help with Array?

I'm trying to write a function that validates a simple form submission. The
values are passed to the function and if any values are null, the
appropritate error text is added to an array rather than raising the
exception immdediately. If the array is not empty, the function passes its
contents to another function that raises all errors at once to the client.
In theory, anyway. I cannot correctly declare and add values to the plpgsql
array properly. Any help in the right direction is greatly appreciated.