Run attached test
Result:
java version "14-ea" 2020-03-17
Java(TM) SE Runtime Environment (build 14-ea+21-927)
Java HotSpot(TM) 64-Bit Server VM (build 14-ea+21-927, mixed mode, sharing)
MONTH - NARROW_STANDALONE - All name:null
MONTH - NARROW_STANDALONE - Current:N
DAY_OF_WEEK - NARROW_STANDALONE - All name:null
DAY_OF_WEEK - NARROW_STANDALONE - Current:M
The sample uses de as instance. Actually this issue happens on some locales.

Expected Result:
Should return a Map containing all names of the calendar field in the given style and locale and their corresponding field values, instead of null.