add_filter('et_pb_module_shortcode_attributes', 'dbcAllowEmptyButtonText', 10, 3);
function dbcAllowEmptyButtonText($props, $atts, $render_slug) {
if ($render_slug !== 'et_pb_button') return $props;
if (!is_array($props)) return $props;
if (!empty($props['button_text'])) return $props;
$props['button_text'] = ' ';
return $props;
}