public function sanitize_ignored_themes( $value ) {
		$value = (array) $value;
		$valid_slugs = array_values( wp_list_pluck( wp_get_themes(), 'stylesheet' ) );
		$invalid_slugs = array_diff( $value, $valid_slugs );

		if ( ! empty( $invalid_slugs ) ) {
			add_settings_error(
				'soter_ignored_plugins',
				'invalid_soter_ignored_plugins',
				sprintf(
					'Only currently installed themes can be ignored. The following invalid theme slugs were provided: %s',
					implode( ', ', array_map( 'esc_html', $invalid_slugs ) )
				)
			);

			return $this->ignored_themes;
		}

		return $value;
	}