def create
      if exists?
        raise InvalidPathError, "workspace #{@namespace} is already exists"
      end
      FileUtils.mkdir_p(namespace_dirname)
      @version_manager.init
      root.create
    end
def create
      if exists?
        raise InvalidPathError, "workspace #{@namespace} is already exists"
      end
      FileUtils.mkdir_p(namespace_dirname)
      @version_manager.init
      root.create
    end
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