Maybe
x=> x.Lists.Include(l => l.Title)
.Where(l => l.Title != string.Empty)
.Where(l => l.InternalName != string.Empty)
?
You can probably also put it in the same where clause:
x=> x.Lists.Include(l => l.Title)
.Where(l => l.Title != string.Empty && l.InternalName != string.Empty)