code: public OkRequest<T> form(final Map<String, String> values, final String charset) {
          if (!values.isEmpty()) {
              for (Map.Entry<String, String> entry : values.entrySet()) {
                  form(entry, charset);
              }
          }
          return this;
      }
docs: Write the values in the map as encoded form data to the request body
  
  @param values
  @param charset
  @return this request