_.defaultsDeeps return and mutate behaviour is inconsistent with null object

[TechWilk]

I'm getting inconsistent behaviour in defaultsDeep between the mutated object and the return value.

let a = null;
const b = {this: "that"};

// Note: This method mutates object `a`
const c = _.defaultsDeep(a, b);

console.log(a); // null
console.log(c); // {this: "that"};

According to the docs, I would expect both a and c to be the same value once defaultsDeep has been called.

_.defaultsDeep(object, [sources])
[source](https://github.com/lodash/lodash/blob/4.17.15/lodash.js#L12836) [npm package](https://www.npmjs.com/package/lodash.defaultsdeep)

This method is like [_.defaults](https://lodash.com/docs/#defaults) except that it recursively assigns default properties.

Note: This method mutates object.

Since

3.10.0

Arguments

object (Object): The destination object.
[sources] (...Object): The source objects.
Returns

(Object): Returns object.