Single nested document set function is being calling twice

[LucGranato]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When setting a value to a single nested document field

rootDoc.set('anything.subDoc.someField', 12);

The set function is called twice

{
  ...
  someField: {
    set: function(value) {
      return value;
    }
  }
  ...
}

The first time with this as rootDoc and the second as subDoc.

If the current behavior is a bug, please provide the steps to reproduce.
RunKit Example

What is the expected behavior?
Calling only one time.

Please mention your node.js, mongoose and MongoDB version.
node: 8.11.3
mongoose: 5.3.7

[vkarpov15]

Thanks for reporting, will fix asap