code: @Override
      public Header getResponseHeader(String headerName) {        
          if (headerName == null) {
              return null;
          } else {
              return getResponseHeaderGroup().getCondensedHeader(headerName);
          }        
      }
docs: Gets the response header associated with the given name. Header name
  matching is case insensitive. <tt>null</tt> will be returned if either
  <i>headerName</i> is <tt>null</tt> or there is no matching header for
  <i>headerName</i>.
  
  @param headerName the header name to match
  
  @return the matching header