ModelMerger$MergingList is not serializable

Hello!

Spotless Maven plugin serializes org.apache.maven.model.Plugin instances to fingerprint plugin's configuration. Serialization fails for Maven 3.6.3 with:

java.io.NotSerializableException: org.apache.maven.model.merge.ModelMerger$MergingList

when plugin configuration comes from pluginManagement. Class org.apache.maven.model.Plugin implements java.io.Serializable, however nested class org.apache.maven.model.merge.ModelMerger$MergingList does not.

Would it be possible to make MergingList serializable or make Plugin#dependencies field always hold a serializable collection?

Related issue for the Spotless Maven plugin: https://github.com/diffplug/spotless/issues/1073 and PR with a workaround https://github.com/diffplug/spotless/pull/1074.

Thank you!