NullPointerException when two fields we have same key, itemProvider, namePrefix..

Steps to reproduce

1. Create a dialog like the one in the picture
2. Export and import content using the content translation app

Getting NullPointerException when a multivalue field contains extra fields that should not be translated.

java.lang.NullPointerException: null
	at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1470) ~[?:?]
	at java.text.DateFormat.parse(DateFormat.java:393) ~[?:?]
	at info.magnolia.translation.io.TranslationItem$Builder.withLastModificationTime(TranslationItem.java:184) ~[magnolia-content-translation-2.5.1.jar:?]

Duplicated keys can be generated with different combination of itemProvider (current, child) and propertyNameDecorator (switchable field) or simple fields (attached example yml):

Expected results

Import without an error

Actual results

NullPointerException

Workaround

There is no workaround

Development notes