Notice: Trying to get property of non-object

Hello,

Great work, it works well, and when I tried to debug, it show some error message:

Notice: Trying to get property of non-object in /var/www/mysite.com/htdocs/wp-content/plugins/fv-gravatar-cache/fv-gravatar-cache.php on line 197

Pleae check the screenshot at https://prntscr.com/e0jxb1

We are running a wordpress Mu sites, and whatever it is network or alone site activated, those messages will always show up. You might kindly let me how to resolve it.

Thanks.

Alex