implode(): Invalid arguments passed in…

Hi!

I am struggling with a feature in the Optimizer theme free version.

In this feature:
“Display posts from these categories only”
– You can select a item (category) to only view those posts.

if(!empty($optimizer[‘posts_cat_id’])){
$postcat = $optimizer[‘posts_cat_id’];
set_query_var( ‘cat’, ”.implode(‘,’, $postcat).” );
}

I get this warning:
– Warning: implode(): Invalid arguments passed in themes/optimizer/lib/functions/core.php on line 25

Line 25 is – set_query_var( ‘cat’, ”.implode(‘,’, $postcat).” );

http://stevenkas.no