I have a question regarding mail setting metamta.placeholder-to-recipient It says "If no value is set, messages with no To will have their CCs upgraded to To."

The problem is I created a personal herald rule to send me an email when a certain author commits. The rule passes but the mail delivery fails. When I look at the details under Metadata I see the following

Message PHID PHID-XXXX-xxxxxxxxxxxxxx
Status Details Invalid address: null
Actor XYZ
Related Object rXXxxxxxx: - zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

To test if empty "metamta.placeholder-to-recipient" is causing the problem I added some email ID to it and resent (using ./bin/mail resend) the mail, it works perfectly, the mail is sent.

Now my question is shouldn't the CC's be upgraded to To here ? If its not automatic how do I do it ? I didn't see any config for that.

These are the version details

phabricator 77d543ba44638a2e43e1b6bb7f75db80b4046409 (Sat, May 21)
arcanist 0249f90a9a4aa42da0823673a6ac8c620251d82a (Sat, May 21)
phutil 7ff4bd8dfb0b58686a72821dd0e9e79e0f5cbbb9 (Sat, May 21)
Local Version Bitnami Phabricator 20160523-0

I don't know if this is a bug or I am missing something so posted it as a question. Any pointers will be helpful.

Thanks,
Vivekanand.