NAPTR last field "." is misinterpreted as not-a-FQDN

When posting an NAPTR record, the ods-signer expands its last field ("Replacement") with the zone name to form a FQDN. It is however common practice to use a single . in this field to avoid having to specify an actual resource.

Input: @ IN NAPTR 30 10 "u" "E2U+sms:mailto" "Unable to render embedded object: File (mms@example.com) not found." "."

Output: 1.2.3.4.5.e164.arpa. 3600 IN NAPTR 30 10 "u" "E2U+sms:mailto" "Unable to render embedded object: File (mms@example.com) not found." ".".1.2.3.4.5.e164.arpa.

The "." is probably seen as a single label, and thus as something to expand upon. That would be correct for all other forms but this single dot, which AFAIK is a valid FQDN.

In RFC 2915, both "Example 1" and "Example 2" show a use of this field, which is flag-dependent, and they show a single dot in this field where none of the suitable flags are used.