Why Every User Without a Profile Picture on GitHub Was Yehuda Katz

In 2013, GitHub experienced a bug that caused every user without a profile photo to be assigned the profile photo of a specific user, Yehuda Katz, who is a well-known software developer and member of the Ruby on Rails core team.The reason for this was because the Ruby programming language assigns the ID of 4 to nil, which is a special value that represents the absence of a value. Yehuda Katz's user ID on GitHub happened to be 4, and the bug in GitHub's code caused it to assign his profile photo to any user who had not uploaded their own profile photo.