Unsupported operand types

PHP Fatal error: Unsupported operand types in wp-content/plugins/custom-taxonomy-templates/custom-taxonomy-templates.php on line 175

I change the line to :
$templates .= $this->get_templates( $theme->get_template() );

and it’s work.

https://wordpress.org/plugins/custom-taxonomy-templates/