fixed CNFE with site:run

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608549 13f79535-47bb-0310-9956-ffa450edef68
release cancelled

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608553 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare release maven-site-plugin-3.4

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608556 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608558 13f79535-47bb-0310-9956-ffa450edef68
This unittest would have found the cause of the failing site:run discovered by jieryn as exposed by Release Apache Maven Site Plugin version 3.4 Take 1

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608582 13f79535-47bb-0310-9956-ffa450edef68