Dom4j is included as a dependency in Vitro, but it does not appear to be used in any way.
The project home page https://dom4j.github.io/ indicates that the most recent version is 2.0 beta, for Java 1.5.
Dom4j 1.6.1 (the version currently in VIVO), depends on xml-apis-1.0b2. This package contains classes in org.w3c.dom which conflict with the matching classes in Java 1.8. This can produce compile or runtime errors, depending on the classpath ordering.