PHP long running foreach traverses null memory overflow?

<code>while (1){
    echo memory_get_usage();
    echo ';';
    foreach(null as $each){
        echo 1;
    }
    sleep(1);
}</code>

The console output shows that the memory usage continues to increase. Replacing null with [] will not cause this phenomenon. Seek to explain?

Reply content:

<code>while (1){
    echo memory_get_usage();
    echo ';';
    foreach(null as $each){
        echo 1;
    }
    sleep(1);
}</code>

The console output shows that the memory usage continues to increase. Replacing null with [] will not cause this phenomenon. Seek to explain?

PHP7 environment actual test
Visual inspection shows a warning when the null is reached. .