REST response for long datatype converting from String

I am getting a response from REST service which contains long datatype but Mendix is treating that at string and converting it to Long then which is throwing  NumberFormatException error .

Rest Service Respone :  {"date":"2017-05-08 00:00:00","quantity":-3900000,"item":"food","type":"Others"}

Resposne in Mendix (via log level as Trace) {"date":"2017-05-08 00:00:00","quantity":-3900000.0,"item":"food","type":"Others"}

datatype of quantity in import mapping and mendix entity is long and i don't know from where the decimal part is adding to it which is throwing the exception.