simple php question on adding variables to an array.

This is driving me bonkers. I thought I understood this. I am pulling nodes out of the database, then simply comparing a field, if true, then add to an array, then return the array as multiple arguments to exlude from a view..

 if ( $collab_note_nid->field_collab_note_nursing[0]['nid'] == $my_nurse_nid){
                    array_push($time_block_array, $collab_note_nid->field_collab_note_time[0]['nid']); 
        }
$time_block_array = array_unique($time_block_array);
return implode('+', $time_block_array);

My array return is the problem. It is coming in as
+453+467

I need 453+467. I must be adding a null value to the array. Is there a simple way to strip that out, or a better way to return the nids as 453+467?

Thanks a ton. Worked all day on this.