How to pass an empty contentCharset to streamResult

Hello,
I’m facing an issue and I think it’s a “bug” on StreamResult (not sure about it however).

I know I can pass or do not pass a parameter contentCharSet on the result in struts.xml. If I do not pass it, for some reason I find UTF-8 is added automatically.

However if I do pass a value that is an expression I would expect that if the expression evaluates to null, the charset would not be added to the headers.
What happens instead is that a 

;charSet=

string is added to the content type.

The “bug” is likely related to this code in StreamResult.java

            if (contentCharSet != null && !contentCharSet.isEmpty()) {
                oResponse.setContentType(conditionalParse(contentType, invocation) + ";charset=" + conditionalParse(contentCharSet, invocation));
            } else {
                oResponse.setContentType(conditionalParse(contentType, invocation));
            }

So my questions are :

1. why I find UTF-8 if I don’t specify the parameter;
2. shouldn’t the if check the emptiness of the evaluated expression in the code above ?

Thanks
— 
Ing. Andrea Vettori
Sistemi Informativi
B2BIres s.r.l.