private String unquote(String value) {
    if (value == null) {
      return null;
    }
    return isSurroundedBy(value, "\"") || isSurroundedBy(value, "'")
        ? value.substring(1, value.length() - 1)
        : value;
  }
Construct an {@code AbstractHttpMessageConverter} that can read mulitpart/form-data.

@param bufSize The size of the buffer (in bytes) to read the HTTP multipart body.
form-spring/src/main/java/feign/form/spring/converter/SpringManyMultipartFilesReader.java