code: public final void setHttpMethod(HttpMethod httpMethod) {
          if (overriddenURL != null && httpMethod != HttpMethod.GET) {
              throw new FacebookException("Can't change HTTP method on request with overridden URL.");
              }
          this.httpMethod = (httpMethod != null) ? httpMethod : HttpMethod.GET;
      }
docs: Sets the {@link HttpMethod} to use for this request.
  
  @param httpMethod
  the HttpMethod, or null for the default (HttpMethod.GET).