code: public HttpRequest withBody(String body, Charset charset) {
          if (body != null) {
              this.body = new StringBody(body, charset);
          }
          return this;
      }
docs: The exact string body to match on such as "this is an exact string body"
  
  @param body    the body on such as "this is an exact string body"
  @param charset character set the string will be encoded in