Failed to translate JSON to XML in BPEL Process

Hello all ,

now i exposed rest service from Oracle SOA 12 and when i call this service with the following json request

{

"var1" : "value1",

"var2": "value2"

}

it is executed successfully but my problem is when i call this service with the following json request

{

"var1": "" ,

"var2" : "value2"

}

the following exception occurred "{"RestFaultElement":{"summary":"Translation Failure.\nFailed to translate JSON to XML. cannot normalize! The incoming data does not conform to the NXSD schema. Please correct the problem.\n","code":null,"detail":null}}"

how to ignore empty values in json request in BPEL receive activity ????