Array Null

In personalize mode, this news appears. The code is as follows. What should I change?

p.s. The code in bold corresponds to the line to be corrected

Thank you very much for your help

Notice: Trying to access array offset on value of type null in?/Applications/MAMP/htdocs/romana-avellino/wp-content/themes/mesmerize-pro/inc/companion.php?on line?156 e 149

public static function check_companion( $wp_customize ) {

$plugin_state = self::$plugin_state;

if ( ! $plugin_state['installed'] || ! $plugin_state['active'] ) {

$wp_customize->add_setting( 'companion_install', array(

'default' => '',

'sanitize_callback' => 'esc_attr',

) );

if ( ! $plugin_state['installed'] ) {

$wp_customize->add_control(

new Install_Companion_Control(

$wp_customize,

'mesmerize_page_content',

array(

'section' => 'page_content',

'settings' => 'companion_install',

'label' => self::$config['install_label'],

'msg' => self::$config['install_msg'],

'plugin_state' => $plugin_state,

'slug' => self::$slug,

)

)

);

} else {

$wp_customize->add_control(

new Activate_Companion_Control(

$wp_customize,

'mesmerize_page_content',

array(

'section' => 'page_content',

'settings' => 'companion_install',

'label' => self::$config['activate_label'],

'msg' => self::$config['activate_msg'],

'plugin_state' => $plugin_state,

'slug' => self::$slug,

)

)

);

}

Companion_Plugin::show_companion_popup( $plugin_state );

}

}