Iterating on an empty `SynapseCollection` raises `TypeError: 'NoneType' object is not iterable`

[CircuitCoder]

Describe the bug Iterating on an empty SynapseCollection raises TypeError: 'NoneType' object is not iterable.

It seems that this is caused by:

1. When SynapseCollection is empty, its _datum field is None
2. Constructor of SynapseCollectionIterator doesn't check for this case.

To Reproduce Steps to reproduce the behavior:

>>> s = nest.SynapseCollection(None)
>>> for row in s:
...     pass
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/nest/lib/python3.10/site-packages/nest/lib/hl_api_types.py", line 608, in __iter__
    return SynapseCollectionIterator(self)
  File "/opt/nest/lib/python3.10/site-packages/nest/lib/hl_api_types.py", line 567, in __init__
    self._iter = iter(synapse_collection._datum)
TypeError: 'NoneType' object is not iterable

Expected behavior SynapseCollectionIterator creates an empty iterator when the collection is empty.

Desktop/Environment (please complete the following information):

• OS: Ubuntu 22.04
• Shell: bash
• Python-Version: 3.10.12
• NEST-Version: 3.5.0
• Installation: docker

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Issue automatically marked stale!