property of non-object, missing subject error notices

After sending an email, I get error notices:

Notice: Trying to get property of non-object in send_mails_form_submit() (line 137 of /home/mysite/public_html/sites/all/modules/send_mails/send_mails.form.inc).
Notice: Trying to get property of non-object in send_mails_form_submit() (line 138 of /home/mysite/public_html/sites/all/modules/send_mails/send_mails.form.inc).
Notice: Trying to get property of non-object in send_mails_form_submit() (line 139 of /home/mysite/public_html/sites/all/modules/send_mails/send_mails.form.inc).

In addition, I'm using Mail Logger → , and in the Mail Logger log, the sent emails show up, but the subject reads "Missing subject."

The emails DO get sent and received, and the recipient does see the subject line.

I believe this happens in both 7.x-2.x-dev and also 7.x-1.0.

Thanks!