Prevent "SyntaxError: Empty JSON string (null$lib#3)" error on a 'POST' request to a RESTlet with content-type:application/json

To resolve the "SyntaxError: Empty JSON string (null$lib#3)" error on a 'POST' request to a RESTlet, make sure that there is a valid JSON object on the request body. The system looks for a JSON object in the request body if the HTTP method is 'POST'.