Java 8 Parse ISO-8601 date ignoring presence (or absence) of timezone

Question

My application should be able to parse date ignoring timezone (I always know for sure that it is UTC). The problem is that the date might come in both following forms -

2017-09-11T12:44:07.793Z

0001-01-01T00:00:00

I can parse the first one using LocalDateTime, and the second one using Instant class. Is there a way to do that using a single mechanism?

P.S. I'm trying to avoid hardcoding Z at the end of the input string