code: @Override
      public Header getRequestHeader(String headerName) {
          if (headerName == null) {
              return null;
          } else {
              return getRequestHeaderGroup().getCondensedHeader(headerName);
          }
      }
docs: Returns the specified request header. Note that 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 name of the header to be returned.
  
  @return The specified request header.
  
  @since 3.0