OAK-798: Review / refactor TreeImpl and related classes
Replace usages of Root.getTreeOrNull with Root.getTree
Replace usages of Tree.getChildOrNull with Tree.getChild

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1477545 13f79535-47bb-0310-9956-ffa450edef68
OAK-798: Review / refactor TreeImpl and related classes
Replace Root.getLocation with Root.getTree
Replace Tree.getChildOrNull with Tree.getChild

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1477546 13f79535-47bb-0310-9956-ffa450edef68