Currently, the specification for clCommandNDRangeKernelKHR says:

kernel is a valid kernel object which must have its arguments set.

This is indeed true if cl_khr_command_buffer_mutable_dispatch is not supported. However, our implementation does support this extension, and in our use cases, we don't know at least some of the kernel's arguments at recording time.
I suggest to specify in cl_khr_command_buffer_mutable_dispatch that when recording an ND-range kernel command, kernel's arguments don't have to be set (of course, all of them must be set when the command buffer is replayed).