**Hi, my name is riyan, im quite new in pypsa. i made my own network consist of Medium and Low voltage in Indonesia to check the loading of transformer and line, but also checking the voltage on the end of radial network. i already succeded build pypsa network, an also i’m running pypsa network.lpf() everything fine. and when i try to do network.pf() for non linear power flow , with one generator slack. and MV and LV network.
it give me error like this, can you explain it why or how to solve it:
**

`**KeyError**                                  Traceback (most recent call last)
File ~anaconda3envsdissertationLibsite-packagespandascoreindexesbase.py:3805, in Index.get_loc(self, key)
   3804 try:
-> 3805     return self._engine.get_loc(casted_key)
   3806 except KeyError as err:

File index.pyx:167, in pandas._libs.index.IndexEngine.get_loc()

File index.pyx:196, in pandas._libs.index.IndexEngine.get_loc()

File pandas\_libs\hashtable_class_helper.pxi:7081, in pandas._libs.hashtable.PyObjectHashTable.get_item()

File pandas\_libs\hashtable_class_helper.pxi:7089, in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: None

The above exception was the direct cause of the following exception:

---
File ~anaconda3envsdissertationLibsite-packagespypsapf.py:263, in network_pf(network, snapshots, skip_pre, x_tol, use_seed, distribute_slack, slack_weights)
    216 def network_pf(
    217     network,
    218     snapshots=None,
   (...)
    223     slack_weights="p_set",
    224 ):
    225     """
    226     Full non-linear power flow for generic network.
    227 
   (...)
    260         iteration error for each snapshot (rows) and sub_network (columns)
    261     """
--> 263     return _network_prepare_and_run_pf(
    264         network,
    265         snapshots,
    266         skip_pre,
    267         linear=False,
    268         x_tol=x_tol,
    269         use_seed=use_seed,
    270         distribute_slack=distribute_slack,
    271         slack_weights=slack_weights,
    272     )

File ~anaconda3envsdissertationLibsite-packagespypsapf.py:192, in _network_prepare_and_run_pf(network, snapshots, skip_pre, linear, distribute_slack, slack_weights, **kwargs)
    183     sub_network_pf_fun(
    184         sub_network, snapshots=snapshots, skip_pre=True, **kwargs
    185     )
    187 elif len(sub_network.buses()) <= 1:
    188     (
    189         itdf[sub_network.name],
    190         difdf[sub_network.name],
    191         cnvdf[sub_network.name],
--> 192     ) = sub_network_pf_singlebus(
    193         sub_network,
    194         snapshots=snapshots,
    195         skip_pre=True,
    196         distribute_slack=distribute_slack,
    197         slack_weights=sn_slack_weights,
    198     )
    199 else:
    200     (
    201         itdf[sub_network.name],
    202         difdf[sub_network.name],
   (...)
    210         **kwargs,
    211     )

File ~anaconda3envsdissertationLibsite-packagespypsapf.py:411, in sub_network_pf_singlebus(sub_network, snapshots, skip_pre, distribute_slack, slack_weights, linear)
    405         network.generators_t.p.loc[
    406             snapshots, group.index
    407         ] += bus_generator_shares.multiply(
    408             -network.buses_t.p.loc[snapshots, bus], axis=0
    409         )
    410 else:
--> 411     network.generators_t.p.loc[
    412         snapshots, sub_network.slack_generator
    413     ] -= network.buses_t.p.loc[snapshots, sub_network.slack_bus]
    415 network.generators_t.q.loc[
    416     snapshots, sub_network.slack_generator
    417 ] -= network.buses_t.q.loc[snapshots, sub_network.slack_bus]
    419 network.buses_t.p.loc[snapshots, sub_network.slack_bus] = 0.0

File ~anaconda3envsdissertationLibsite-packagespandascoreindexing.py:1184, in _LocationIndexer.__getitem__(self, key)
   1182     if self._is_scalar_access(key):
   1183         return self.obj._get_value(*key, takeable=self._takeable)
-> 1184     return self._getitem_tuple(key)
   1185 else:
   1186     # we by definition only have the 0th axis
   1187     axis = self.axis or 0

File ~anaconda3envsdissertationLibsite-packagespandascoreindexing.py:1368, in _LocIndexer._getitem_tuple(self, tup)
   1366 with suppress(IndexingError):
   1367     tup = self._expand_ellipsis(tup)
-> 1368     return self._getitem_lowerdim(tup)
   1370 # no multi-index, so validate all of the indexers
   1371 tup = self._validate_tuple_indexer(tup)

File ~anaconda3envsdissertationLibsite-packagespandascoreindexing.py:1065, in _LocationIndexer._getitem_lowerdim(self, tup)
   1061 for i, key in enumerate(tup):
   1062     if is_label_like(key):
   1063         # We don't need to check for tuples here because those are
   1064         #  caught by the _is_nested_tuple_indexer check above.
-> 1065         section = self._getitem_axis(key, axis=i)
   1067         # We should never have a scalar section here, because
   1068         #  _getitem_lowerdim is only called after a check for
   1069         #  is_scalar_access, which that would be.
   1070         if section.ndim == self.ndim:
   1071             # we're in the middle of slicing through a MultiIndex
   1072             # revise the key wrt to `section` by inserting an _NS

File ~anaconda3envsdissertationLibsite-packagespandascoreindexing.py:1431, in _LocIndexer._getitem_axis(self, key, axis)
   1429 # fall thru to straight lookup
   1430 self._validate_key(key, axis)
-> 1431 return self._get_label(key, axis=axis)

File ~anaconda3envsdissertationLibsite-packagespandascoreindexing.py:1381, in _LocIndexer._get_label(self, label, axis)
   1379 def _get_label(self, label, axis: AxisInt):
   1380     # GH#5567 this will fail if the label is not present in the axis.
-> 1381     return self.obj.xs(label, axis=axis)

File ~anaconda3envsdissertationLibsite-packagespandascoregeneric.py:4287, in NDFrame.xs(self, key, axis, level, drop_level)
   4285 if axis == 1:
   4286     if drop_level:
-> 4287         return self[key]
   4288     index = self.columns
   4289 else:
File ~anaconda3envsdissertationLibsite-packagespandascoreframe.py:4102, in DataFrame.__getitem__(self, key)
   4100 if self.columns.nlevels > 1:
   4101     return self._getitem_multilevel(key)
-> 4102 indexer = self.columns.get_loc(key)
   4103 if is_integer(indexer):
   4104     indexer = [indexer]

File ~anaconda3envsdissertationLibsite-packagespandascoreindexesbase.py:3812, in Index.get_loc(self, key)
   3807     if isinstance(casted_key, slice) or (
   3808         isinstance(casted_key, abc.Iterable)
   3809         and any(isinstance(x, slice) for x in casted_key)
   3810     ):
   3811         raise InvalidIndexError(key)
-> 3812     raise KeyError(key) from err
   3813 except TypeError:
   3814     # If we have a listlike key, _check_indexing_error will raise
   3815     #  InvalidIndexError. Otherwise we fall through and re-raise
   3816     #  the TypeError.
   3817     self._check_indexing_error(key)

KeyError:None

can you help me solve this or tell me why its happen? seems like pyspa can not detect the slack bus or slack generator, while i already define generator control as 'Slack'. it still gives me 'None' key error. it works really well if i only use network.lpf() but when i use non linear network.pf() it keeps giving me error
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