Send email review to LDAP user (without defined email address) creates NullPointerException

In Crucible review, if I send email review to built-in user (without defined email address) will prompt correct error message. To reproduce, follow steps below:

1. Select one existing review.
2. Click on "Email Review" button.
3. Enter a recipient (built-in user) who has blank email value in the user record.
4. Click "Send" button.
5. The exception is "javax.mail.SendFailedException - No recipient addresses" on the same screen.

But if we choose to send to LDAP user with similar situation, NPE is being thrown.

1. Select one existing review.
2. Click on "Email Review" button.
3. Enter a recipient (LDAP user) who has blank email value in the user record.
4. Click "Send" button.
5. The exception is "javax.lang.NullPointerException" on the another screen with "500 Server Error".