java - Reading json input on Jersey which can be both nullable and optional -

i have following rest end-point

@put @path("/props") public response update(props input) { .. } 

and input parameter is:

@xmlaccessortype(xmlaccesstype.field) class props {     public string prop1;     public string prop2; } 

client sends input json string. want both parameter nullable , optional. example: if client wants update prop2 null value without updating prop1 may send:

{"prop2":null} 

but @ point see both input.prop1 = null , input.prop2 = null.

how can distinguish if client has sent prop null value or has not sent @ all?

isn’t better make empty string if want set null, , null if did not sent @ all?