The XML schema definition of the host.storage_domain_extensions specifies "unbounded" for the "maxoccurs" attribute. This is wrong, and as a result the getter method of the Java class generated by the XJC compiler returns a list:

  List<StorageConnectionExtensions> getStorageConnectionExtensions() {
    ...
  }

This isn't an issue for the server, as this method isn't used at all. But it induces a compilation error in the Java SDK because the code generator assumes that this method returns only one element, and the code generated for the host decorator overrides it as follows:

  HostStorageConnectionExtensions getStorageConnectionExtensions() {
    ...
  }

The XML schema needs to be modified so that the value of maxoccurs is 1 instead of unbounded.