ak.where errors if array has None

[timdiller]

Version of Awkward Array

2.6.5

Description and code to reproduce

In version 2.0.7 I could do something like this:

import numpy as np
import awkward as ak
a = np.arange(12.).reshape(3,4)
a[2,3] = np.nan
b = ak.nan_to_none(a)
ak.where(b == ak.max(b))

With a result like this:

(<Array [2] type='1 * int64'>, <Array [2] type='1 * int64'>)

In version 2.6.4 and 2.6.5 I get an error like this:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/_dispatch.py", line 64, in dispatch
    next(gen_or_result)
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/operations/ak_where.py", line 55, in where
    return _impl1(condition, mergebool, highlevel, behavior, attrs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/operations/ak_where.py", line 74, in _impl1
    out = layout.backend.nplike.nonzero(layout.to_backend_array(allow_missing=False))
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/contents/content.py", line 1020, in to_backend_array
    return self._to_backend_array(allow_missing, backend)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/contents/regulararray.py", line 1277, in _to_backend_array
    out = self._content._to_backend_array(allow_missing, backend)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/timdiller/test_environment/lib/python3.12/site-packages/awkward/contents/indexedoptionarray.py", line 1609, in _to_backend_array
    raise ValueError(
ValueError: Content.to_nplike cannot convert 'None' values to np.ma.MaskedArray unless the 'allow_missing' parameter is set to True

This error occurred while calling

    ak.where(
        <Array [[False, False, False, False], ..., [...]] type='3 * 4 * ?bool'>
    )

There is no place I can find to pass allow_missing.

This seems to be something different from #3098.