Passing None to Python task triggers Future error

[elliottslaughter]

I accidentally passed a None through to one of my Python tasks and observed the following error. Presumably this means some error checking is missing at the call site.

To be clear: I don't expect this to work but it could be more ergonomic:

1. The error message doesn't match what the user is doing
2. The backtrace is a C++ backtrace, but the error could have been caught in Python (resulting in a Python backtrace) before calling into C++

Reproducer:

import numpy as np
import cupynumeric as cpn

from legate.core import VariantCode, broadcast
from legate.core.task import task, InputArray

@task(variants=(VariantCode.CPU,), constraints=(broadcast("x"),))
def asdf(x: InputArray):
    x = np.asarray(x)

asdf(None)

$ legate --cpus=1 --omps=0 --gpus=0 --sysmem=30000 ../../helios/test_ret_none.py
[0 - 1548100a8740]    0.623558 {5}{runtime}: LEGION ERROR: Future size mismatch! Expected non-empty future for making an accessor but future has a payload of
0 bytes. (UID 0) (from file /tmp/conda-croot/legate/work/arch-conda/skbuild_core/_deps/legion-src/runtime/legion/runtime.cc:1217)
Signal 6 received by node 0, process 1204856 (thread 1548100a8740) - obtaining backtrace
Signal 6 received by process 1204856 (thread 1548100a8740) at:

Version:

$ legate-issue 
System info:
  Python      :  3.13.5 | packaged by conda-forge | (main, Jun 16 2025, 08:27:50) [GCC 13.3.0]
  Platform    :  Linux-4.18.0-553.71.1.el8_10.x86_64-x86_64-with-glibc2.28
  GPU driver  :  (failed to detect)
  GPU devices :  (failed to detect)

Package versions:
  legion      :  25.8.0 (commit: 16441d05a66bdf0f21e271b943a60315f113a55e)
  legate      :  25.09.00.dev0
  cupynumeric :  25.09.00.dev+8.gd1f6b2e4
  numpy       :  2.3.2
  scipy       :  1.16.1
  numba       :  (failed to detect)

Package details:
  cuda-version : (conda missing)
  legate       : (conda missing)
  cupynumeric  : (conda missing)

Legate build configuration:
  build_type        : Release
  use_openmp        : True
  use_cuda          : False
  networks          : ucx
  conduit           : 
  configure_options : --LEGATE_ARCH=arch-conda;--with-python;--with-cc=/tmp/conda-croot/legate/_build_env/bin/x86_64-conda-linux-gnu-cc;--with-cxx=/tmp/conda-croot/legate/_build_env/bin/x86_64-conda-linux-gnu-c++;--build-march=x86-64;--cmake-generator=Ninja;--with-openmp;--with-cuda=0;--build-type=release;--with-ucx

LANL/SLAC low priority.