The cascade selector selects multiple selection{   Multiple: true} and any one level option {checkstrict: true} will be invalid when you click , and an error will be reported as follows

Cascade selection has strict requirements on data. Each data item contains at least two items: value and label, and the subset is children </ Font> the data styles provided on the official website are as follows:

Here is my data on the console

When I change the value of value from int type to string type, I will not report an error. See the figure below for details.

The simplest way is + “, when any type is added to string, it will be converted to string first