背景：在本地初始化了一个Git代码仓库，关联到Github上新建的仓库，第一次执行git pull origin master 拉取远程分支时，出现标题上的问题（Git 2.9之后的版本才会出现此问题）。
原因："git merge" used to allow merging two branches that have no common base by default, which led to a brand new history of an existing project created and then get pulled by an unsuspecting maintainer, which allowed an unnecessary parallel history merged into the existing project. The command has been taught not to allow this by default, with an escape hatch "--allow-unrelated-histories" option to be used in a rare event that merges histories of two projects that started their lives independently（stackoverflow）.
问题的结局方法，在git pull origin master后面跟上参数--allow-unrelated-histories
原因:“git合并”用于允许合并两个分支没有公共基础在默认情况下,导致了一个全新的历史的一个现有的项目创建然后被拉毫无戒心的维护者,这允许一个不必要的平行历史合并到现有的项目。突击队员被告知默认情况下不允许这样做，有一个escape hatch“——allowunrelated- history”选项，用于罕见的事件，合并两个项目的历史，开始他们的生活独立(stackoverflow)
