Undefined variable: pong

In 4.7 we get this warning:
Notice: Undefined variable: pong in …/wp-content/plugins/xml-sitemap-feed/includes/class-xmlsitemapfeed.php on line 1188

Here is the fix at line 1188:
v.4.7:

if ( $pong = get_option( $this->prefix.'pong' ) && is_array($pong) ) {

patch:

if ( $pong = get_option( $this->prefix.'pong' ) and is_array($pong) ) {

You could also clarify line 642, though it does work due to PHP’s lax syntax:
v.4.7:

if ( $post_type == 'page' && $id = get_option('page_on_front') ) {

patch:

if ( $post_type == 'page' and $id = get_option('page_on_front') ) {

https://ww.wp.xz.cn/plugins/xml-sitemap-feed/