Uglifier mangle properties has a start_with? undefined error on nil:NilClass

[pickhardt]

There's a bug when I use mangle: properties: true - it just errors with NoMethodError (undefined method `start_with?' for nil:NilClass)

Unfortunately that's all I have. Let me know if there's a debug param you want me to add to get more info. I used this:

    uglifier = Uglifier.new(harmony: true, mangle: {toplevel: true, properties: true})

[lautis]

UglifyJS seems to return something unexpected when used in combination with harmony option. I'm not entirely sure why, and while handling the error better is easy, the new message is not any better.