Kernel set_arg does not accept None

[nlse2]

Describe the bug
The function set_arg called on a kernel does not accept None as an argument even though this is the recommended way to pass a null pointer according to the documentation.

To Reproduce
The following script triggers the problem.

import numpy as np 
import pyopencl as cl 

ctx = cl.create_some_context() 
queue = cl.CommandQueue(ctx) 
mf = cl.mem_flags 

prg = cl.Program(ctx, """ 
__kernel void sum( 
   __global const float *a_g, __global const float *b_g, __global float *res_g) 
{ 
 int gid = get_global_id(0); 
 res_g[gid] = a_g[gid] + b_g[gid]; 
} 
""").build() 

res_g = cl.Buffer(ctx, mf.WRITE_ONLY, 1000) 
knl = prg.sum  # Use this Kernel object for repeated calls 

knl.set_arg(0, res_g) 
knl.set_arg(0, None)

Expected behavior

I expect the code to run without errors but instead I get the following:

Traceback (most recent call last):
File "/root/cl_test.py", line 21, in
knl.set_arg(0, None)

TypeError: set_arg(): incompatible function arguments. The following argument types are supported: 
1. set_arg(self, arg0: int, arg1: object, /) -> None 

Invoked with types: pyopencl._cl.Kernel, int, NoneType

**Environment (please complete the following information):**
- OS: Ubuntu 25.10
- ICD Loader and version: ocl-icd 2.3.3
- ICD and version: pocl 6.0
- CPU/GPU: [e.g. Nvidia Titan V]
- Python version: 3.13.7
- PyOpenCL version: 2026.1.2

**Additional context**
The above script works correctly in pyopencl 2022

[inducer]

See #898. Thanks for the report! I've incorporated part of your reproducer as a test, hope that's OK.

[inducer]

LMK if you need a release with that.