That's not Guava's Iterator.concat(), it's our RdfStream.concat().

Incidentally, there is a useful invocation of Iterators.concat() with one argument. If that arg is an Iterator<Iterator<E>>, concat() will flatten it into an Iterator<E>, which we find useful in our code. See:

https://github.com/futures/fcrepo4/blob/master/fcrepo-kernel/src/main/java/org/fcrepo/kernel/rdf/impl/PropertiesRdfContext.java#L138