code: public void setHeaders(Map<String, List<String>> headerMap) {
          headers = new Headers.Builder();
  
          for (Map.Entry<String, List<String>> e : headerMap.entrySet()) {
              for (String headerValue : e.getValue()) {
                  addHeader(e.getKey(), headerValue);
              }
          }
      }
docs: Sets headers for this resource request. Overrides all headers previously added.
  
  @param headerMap A multimap containing the header names and corresponding values