Update series: add integration test for required "op" field

[0pdd]

The puzzle 785-4e1225ab from #785 has to be resolved:

mystamps/src/main/java/ru/mystamps/web/support/spring/mvc/PatchRequest.java

Line 38 in 7be4e62

// @todo #785 Update series: add integration test for required "op" field

The puzzle was created by Slava Semushin on 24-May-20.