Problem with foreach in Model

[eluser]charlie spider[/eluser]
writing

Code:

$output = $some_stuff;

does two things at once.
it declares the variable $output AND it assigns a value to it.

using .= (dot equals) is the same as writing

Code:

$output = $output + $some_stuff;

which doesn't work because the declaration of $ouput hasn't been finalized yet, so basically you can't add some_stuff to something that doesn't exist yet.