Add the given, single header value under the given name. @param headerName the header name @param headerValue the header value @throws UnsupportedOperationException if adding headers is not supported @see #put(string, List) @see #set(string, string)
See Implementation
Add the given, single header value under the given name. @param headerName the header name @param headerValue the header value @throws UnsupportedOperationException if adding headers is not supported @see #put(string, List) @see #set(string, string)