function deepMergeObjects(first, second) {
	if (second === void 0) {
		return first;
	}

	if (!isObjectNotArray(first) || !isObjectNotArray(second)) {
		return second;
	}

	const result = { ...first, ...second };

	for (const key of Object.keys(second)) {
		if (Object.prototype.propertyIsEnumerable.call(first, key)) {
			result[key] = deepMergeObjects(first[key], second[key]);
		}
	}

	return result;
}
Deeply merges second on top of first, creating a new {} object if needed.
@param {T} first Base, default value.
@param {U} second User-specified value.
@returns {T | U | (T & U)} Merged equivalent of second on top of first.