HttpBuilder bg losing body on failure

Question

I am using HttpBuilder-NG. On error I am getting following response from server.

{ "error": "JsonError", "param": { "obj.instructorId": [ { "msg": "Instructor Not Found", "args": [] } ] } }

But HttpBuilder is losing body. The fromServer object is coming as....

   fromServer = {JavaHttpBuilder$Action$JavaFromServer@3109} 
   is = null
   hasBody = false
   headers = {Collections$UnmodifiableRandomAccessList@3113}  size = 10
   uri = "**********"
   this$1 = {JavaHttpBuilder$Action@3092} 

Code for the error handling is

config.getRequest().getHeaders().put("Authorization","Bearer " + AccessToken);
config.getRequest().getUri().setPath(path);
config.getRequest().setBody(paramValues);
config.getResponse().when(400,(fromServer, o) -> {
    LazyMap lazyMap =  new LazyMap();
    lazyMap.put("error", fromServer.getMessage());
    return lazyMap;
});