_nestedFilter(keys, value) {
    // Get first key from `keys` array, then remove it from array
    const _key = keys.shift()
    // Initialize an empty object
    const _value = {}

    // Convert the keys into a deeply nested object, which the value of the deepest key is
    // the `value` property.
    // Then assign the object to `_value` property.
    setProp(_value, keys, value)

    return [_key, _value]
  }
Nested filter via array-type keys.

@example
const [_key, _value] = this._nestedFilter(keys, value)
this.filters[_key] = _value

@param {string[]} keys - Array-type keys, like `['a', 'b', 'c']`.
@param {*} value - The value to be set.

@return {[]} - An array containing the first key, which is the index to be used in `filters`
object, and a value, which is the nested filter.