Notice: A non well formed numeric value encountered in class.CSSmin.php

Here’s what appears after switching radio buttons in ‘Choose Theme’, on ‘Theme settings’ tab.

( ! ) Notice: A non well formed numeric value encountered in /srv/www/gp66/current/web/app/plugins/democracy-poll/admin/class.CSSmin.php on line 768
Call Stack
#	Time	Memory	Function	Location
1	0.0013	450728	{main}( )	.../options-general.php:0
2	0.0025	494144	require_once( '/srv/www/gp66/current/web/wp/wp-admin/admin.php' )	.../options-general.php:10
3	0.4913	53720760	do_action( )	.../admin.php:212
4	0.4914	53721136	WP_Hook->do_action( )	.../plugin.php:453
5	0.4914	53721136	WP_Hook->apply_filters( )	.../class-wp-hook.php:323
6	0.4914	53722264	Democracy_Poll_Admin->admin_page_load( )	.../class-wp-hook.php:298
7	0.4917	53724896	Democracy_Poll_Admin->update_options( )	.../class.Democracy_Poll_Admin.php:105
8	0.4919	53724480	Democracy_Poll_Admin->update_democracy_css( )	.../class.Democracy_Poll_Admin.php:228
9	0.4919	53724480	Democracy_Poll_Admin->regenerate_democracy_css( )	.../class.Democracy_Poll_Admin.php:544
10	0.4927	53733048	Democracy_Poll_Admin->cssmin( )	.../class.Democracy_Poll_Admin.php:561
11	0.4940	53855160	CSSmin->run( )	.../class.Democracy_Poll_Admin.php:643
12	0.4940	53855160	CSSmin->do_raise_php_limits( )	.../class.CSSmin.php:66
13	0.4940	53855568	CSSmin->normalize_int( )	.../class.CSSmin.php:201