add capability to filter for "empty" or "non-empty" fields in ls-command outputs

The "-filtervalue" parameter allows to filter for particular strings or substrings when using "listing" commands such as lsvdisk, lshost etc.

Currently, the "-filtervalue" parameter syntax does not offer the capability to filter for objects that have particular attribute fields populated at all. So I would like to have the capability to filter for "empty" respectively "non-empty". See below a few example use cases where this functionality would be helpful:

• lsfabricport:
  use case: filter for entries that have e.g. the "host_name" field populated to isolate only ports that are related to existing host objects.
  
  

• lshostports:
  use case: list only hostports for a particular protocol type (i.e. where "nqn" is populated)
  
  

• lsvolume(group)snapshot:
  use case: list only snapshots that have no expiration time set (i.e. where "expiration_time"=empty)

there might be plenty of more examples where it would be nice to be able to filter for empty or non empty. While at some extent it is possible to workaround that with bash syntax and tools such as "grep" etc, REST-API calls cannot be tweaked in that way and hence are depending on the "-filtervalue" capabilities. Same by the way for the filter option in the GUI.

Currently, "filtervalue" only supports wildcard filtering which however requires at least one character to be combined with the "*" wildcard. That does not allow to create filter statements that look for "empty" or "non-empty".

So I would appreciate to get that capability added.