Where did my Nexus 5 camera app icon go?

[AC Question]

Have a nexus 5 that is updated to 5.1.1 and for some reason the camera icon does not appear in the app drawer or on the home screen. Can still open it up from the lock screen and it doesn't appear to be disabled in the apps within settings. Only way I could get it to appear was when I signed into the play store uninstalled the app and then updated. I have tried resetting the phone multiple times and it still won't come back. Any idea why it disappears? I have been googling all day and can't find any answers. I purchased the phone used and replaced the microphone which i don't believe should have anything to do with this. I want to sell the phone, but it seems to be hard to sell a phone "without" a camera app.
Thanks to anyone who can give me some insight on this.