InvalidOperationException: Ignored launch because kernel handle is null only in npm88

[aplainjane]

Hi I have a question when I m running the mpm88 scene ,
error like this

InvalidOperationException: Ignored launch because kernel handle is null
Taichi.ComputeGraph.LaunchAsync (Taichi.Generated.TiNamedArgument[] namedArgs) (at Assets/Taichi/ComputeGraph.cs:37)
Taichi.ComputeGraph.LaunchAsync (System.Collections.Generic.Dictionary`2[TKey,TValue] namedArgs) (at Assets/Taichi/ComputeGraph.cs:53)
Mpm88.Start () (at Assets/Scripts/Mpm88.cs:58)

but the other example run quite well so I don t know how to solve it. And I find that it seems like miss a script "mpm88.kernel.py" i dont know is it the question is. thanks for your help