YANG parser does not allow newline in unique statement

See the attached model.   This model contains a unique statement with a newline:

unique "listkey1
             listkey2";

This produces a parser error in 2.0.7 (it was working in 1.2.3):

Caused by: org.opendaylight.yangtools.yang.parser.spi.source.SourceException: String 'listkey1
listkey2' is not a valid identifier [at /home/verthezp/logs/unique/testmodule.yang:9:4]
at org.opendaylight.yangtools.yang.parser.spi.source.SourceException.throwIf(SourceException.java:99)
at org.opendaylight.yangtools.yang.parser.spi.meta.StmtContextUtils.checkIdentifierString(StmtContextUtils.java:570)
at org.opendaylight.yangtools.yang.parser.spi.meta.StmtContextUtils.parseNodeIdentifier(StmtContextUtils.java:538)
at org.opendaylight.yangtools.yang.parser.rfc7950.stmt.ArgumentUtils.nodeIdentifierFromPath(ArgumentUtils.java:132)
... 43 more

According to what I see in the RFC this should be allowed: see the "unique-arg" and "sep" definitions in https://tools.ietf.org/html/rfc6020#section-12 .