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The default release version is defined in a variable named maven.release.version. The default next snapshot ( maven.development.version) is empty, and calculated by the maven release plugin.
If You usually do not need to do this, but if you want to know what will be the next release will be (or if you want to change it), check the plan variables configuration:
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When you click the 'play' button to kick the release, Bamboo will allow you to customise a few variables. You probably do not need to override anything.
If this module is part of the reference application, other option you might want to override is the global variable 'preparing.refapp.distro.release':
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