Manipulating attributes of an instance resulting from the instances() function will throw an error on computed properties

[spastorclovr]

Bug Report

1. Minimal reproduce step (Required)

https://play.kcl-lang.io/?s=M4YwFgpgtghgBADQE4BM4G0AeqD6BrASwDsUAaAcyQHsBXAB1JABsYCpgBeAMRieAgC6ALgBQccXBh0CANQhJgBKkSHAALkjgc4AIikEImNRCKLlwAHQhqwYHRZEIFpQHoAbgEYdYiYRKqNLV0AYSooOipFYwAlCGBaJBAIABEIADNiAjUlIm8JOCgINRgUGGKhOABvdSQApABfIMqffLgiGEKOHQASSuwUfGIUCyYqAHd5AAoASnqLXspaOnq8iXqWuDsIEArqjSFG7WbWiUX6ILO6Dfz2wuAm65O4PzRtfsGSR-F1jZ+cKToOH6QWQKEmOgQ0QAgnQ6DpSLoAZZLhZjOAdNMqhstiALG55GZTEF0F8sU9WrcIEEdJ5eHQwDAvKT1vkBCIfiJiOoYEQkvdtKDnKZiry4jMRCIcFyRUkgtKeXz0AAGNmS+WiiwvanBAASUIAcgBxACiyR0QA

• Define a Schema with some attributes being "computed" (here it is a lower() call + some concatenation)
• Create an instance
• USe Schame.instances() to retrieve the instances
• Change one attribute of the retrieved instance

2. What did you expect to see? (Required)

I am expecting to be able to change the "kind" attribute.

3. What did you see instead (Required)

invalid value 'NoneType' to load attribute 'lower'

4. What is your KCL components version? (Required)

0.11.2