JSFiddle: https://jsfiddle.net/mem9e9r9/
Error: TypeError: Cannot convert object to primitive value
Description:
It seems like invert() function is triggering an error when converting json object with builtin -> toString property present. I tried with standard JSON files and it does work properly.

It fails to run _.invert() on this JSON object:

{
  "builtin": {
    "toString": false
  }
}