What is better when return false

Hello when using return false I would also like to know if return "" is OK 

Or which one is better over the other.

PHP Code:

public function getattachments($where_column = '', $id = '')
{
 if ($id) {
    $this->db->where($where_column, $id);
 } 

 $query = $this->db->get($this->db->dbprefix . $this->table_name);

 if ($query->num_rows() > 0) {
   return $query->result_array();
 }

 return "";
 
} 


Return an empty array.

Something like return array();

There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!