\prod, \sum with unknown in product/sum term returns NaN

[AdamArwejo]

Steps to Reproduce

import { ComputeEngine } from "@cortex-js/compute-engine";

const ce = new ComputeEngine()
const s = "\\sum_{n=1}^{10}(x)"

const parsed = ce.parse(s)
parsed.evaluate().print()

The error also occurs if \\sum is replaced with \\prod, and regardless of the value of the bounds.

Actual Result

NaN is printed.

Expected Result

10x (in this case) is printed.

Environment

Using @cortex-js/compute-engine version 10.9.0