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Recall the step in which you typed mvn release:prepare. That step introduced two commits in your release branch. Now is the time you need to take the second commit (the one with the comment [maven-release-plugin] prepare for next development iteration) and merge it back to the master.

Or you can run below command to directly update pom version.

$ mvn --batch-mode release:update-versions -DdevelopmentVersion=<next-version>

# example
$ mvn --batch-mode release:update-versions -DdevelopmentVersion=0.4.0-SNAPSHOT

Reference

1. http://plc4x.apache.org/developers/release.html
2. https://cwiki.apache.org/confluence/display/GOBBLIN/Release+Process

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