Missing scripts are now titled "Nothing Selected" (used to be blank) and enabling them throws"ArgumentNullException: Argument cannot be null.Parameter name: key"

2. How we can reproduce it using the example you attached

1) Open attached project and scene Test
2) Delete file "NewBehaviourScript.cs"
3) Select Main Camera and enable script now called "Nothing Selected"
4) Notice error in console

Reproducible in 2017.1.0b1
Not reproducible in 5.6.0f3