code: public GenericResponseBuilder<T> header(String name, Object value) {
      rawBuilder.header(name, value);
      return this;
    }
docs: Adds a header to the response.
  
  @param name the header name
  @param value the header value, {@code null} will clear any existing headers for the same name
  @return this builder
  @see Response.ResponseBuilder#header(String, Object)