@Nullable
        String stringify(@Nullable Object value) {
            if (stringifier == null) {
                return value != null ? value.toString() : null;
            } else {
                return stringifier.apply(value);
            }
        }
Adds the property represented by the specified key pattern to the export list. Please refer to the
<a href="https://armeria.dev/docs/advanced-logging">Logging contextual information</a>
in order to learn how to specify a key pattern.
core/src/main/java/com/linecorp/armeria/common/logging/ExportGroupBuilder.java