Does Array values concat instead of be replaced?

[shell362]

I'm not sure, if this a bug or a feature. Look:

import merge from 'merge-deep';

const object1 = { a: '1', b: '2', c: [1, 2, 3] };
const object2 = { a: undefined, b: null, c: null }; // 'c' property might be anything else, like '1', or undefined, or an empty Array, doesn't matter

const mergedObject = merge(object1, object2);
console.log(mergedObject);
=> { a: undefined, b: null, c: [1, 2, 3] } // So, the last property is not changed.

If 'c' in the object2 was 'abc', we'll get

=> { a: undefined, b: null, c: ['abc', 1, 2, 3] }

It looks like Array type values concat, instead of be replaced with a new value. But I need a tool to replace values while merging.

Should I use assign-deep instead? Cause the last one does it well.