When UPGRADE is used, and we have 2 sites with {A} and {B} as single members of each site, UPGRADE injects view {A,B} when it is activated.

However, this is a virtual view, as B is not in A's real view and vice versa. So when JGroupsTransport.getMembersPhysicalAddresses() tries to get all physical addresses (e.g. in the first site), there will be no physical address for B.

Therefore, JGroupsAddress(Address) will throw an IllegalArgumentException.

It would be better to simply skip the null addresses.