When you click on server -> Cluster name -> in EMC you receive the error
value cannot be null
Parameter name: nodeName
Issue can be caused be a server that is no longer part of the exchange cluster.
You can verify by doing running the following from a elevated EMS prompt
get-clusteredmailboxserverstatus and see if the server with the issue is listed, if not then the solutions is to un-install exchange and re-install as a passive node…. you don’t need to evict from the cluster