generated builder java file for a leaf containing a union needs documentation for why it's stored in src/main/java

This is a shortened example from the TTP repo.

If you have YANG like this:

...
list parameters {
...
leaf default {
type union

}
...
}
...

The DefaultBuilder.java winds up being stored in src/main/java instead of the configured directory.

The same thing happens with PortNumberBuilder.java in controller. Which is generated to opendaylight/md-sal/model/model-flow-base/src/main/java/org/opendaylight/yang/gen/v1/urn/opendaylight/flow/types/port/rev130925/PortNumberBuilder.java

While it's counterparts are generated to opendaylight/md-sal/model/model-flow-base/src/main/yang-gen-sal/org/opendaylight/yang/gen/v1/urn/opendaylight/...