```coffeescript
goog.provide 'app.ValidationError'

class app.ValidationError

  ###*
    @param {string} prop
    @param {string} message
    @constructor
  ###
  constructor: (@prop, @message) ->```

Allow null for app.ValidationError prop.
user
```coffeescript
goog.provide 'app.ValidationError'

class app.ValidationError

  ###*
    @param {?string} prop
    @param {string} message
    @constructor
  ###
  constructor: (@prop, @message) ->```
assistant