code: @Override
      public void addRequestHeader(Header header) {
          LOG.trace("HttpMethodBase.addRequestHeader(Header)");
  
          if (header == null) {
              LOG.debug("null header value ignored");
          } else {
              getRequestHeaderGroup().addHeader(header);
          }
      }
docs: Adds the specified request header, NOT overwriting any previous value.
  Note that header-name matching is case insensitive.
  
  @param header the header to add to the request