prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Note on `Add x.str.cat (#3028)` (lines 125-126)
  It's not clear to me why `String.str.cat` isn't supported in Dask when `others == None`. Not having the ability to concat a single series into a string is a significant cost, I think. Unless there's a reason for this condition, I recommend deleting lines 126-126.
  
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `dask/dataframe/accessor.py`
  Content:
  ```
  1 from functools import partial
  2 
  3 import numpy as np
  4 import pandas as pd
  5 
  6 from ..utils import derived_from
  7 
  8 
  9 def maybe_wrap_pandas(obj, x):
  10     if isinstance(x, np.ndarray):
  11         if isinstance(obj, pd.Series):
  12             return pd.Series(x, index=obj.index, dtype=x.dtype)
  13         return pd.Index(x)
  14     return x
  15 
  16 
  17 class Accessor:
  18     """
  19     Base class for pandas Accessor objects cat, dt, and str.
  20 
  21     Notes
  22     -----
  23     Subclasses should define ``_accessor_name``
  24     """
  25 
  26     _not_implemented = set()
  27 
  28     def __init__(self, series):
  29         from .core import Series
  30 
  31         if not isinstance(series, Series):
  32             raise ValueError("Accessor cannot be initialized")
  33 
  34         series_meta = series._meta
  35         if hasattr(series_meta, "to_series"):  # is index-like
  36             series_meta = series_meta.to_series()
  37         meta = getattr(series_meta, self._accessor_name)
  38 
  39         self._meta = meta
  40         self._series = series
  41 
  42     @staticmethod
  43     def _delegate_property(obj, accessor, attr):
  44         out = getattr(getattr(obj, accessor, obj), attr)
  45         return maybe_wrap_pandas(obj, out)
  46 
  47     @staticmethod
  48     def _delegate_method(obj, accessor, attr, args, kwargs):
  49         out = getattr(getattr(obj, accessor, obj), attr)(*args, **kwargs)
  50         return maybe_wrap_pandas(obj, out)
  51 
  52     def _property_map(self, attr):
  53         meta = self._delegate_property(self._series._meta, self._accessor_name, attr)
  54         token = "%s-%s" % (self._accessor_name, attr)
  55         return self._series.map_partitions(
  56             self._delegate_property, self._accessor_name, attr, token=token, meta=meta
  57         )
  58 
  59     def _function_map(self, attr, *args, **kwargs):
  60         if "meta" in kwargs:
  61             meta = kwargs.pop("meta")
  62         else:
  63             meta = self._delegate_method(
  64                 self._series._meta_nonempty, self._accessor_name, attr, args, kwargs
  65             )
  66         token = "%s-%s" % (self._accessor_name, attr)
  67         return self._series.map_partitions(
  68             self._delegate_method,
  69             self._accessor_name,
  70             attr,
  71             args,
  72             kwargs,
  73             meta=meta,
  74             token=token,
  75         )
  76 
  77     @property
  78     def _delegates(self):
  79         return set(dir(self._meta)) - self._not_implemented
  80 
  81     def __dir__(self):
  82         o = self._delegates
  83         o.update(self.__dict__)
  84         o.update(dir(type(self)))
  85         return list(o)
  86 
  87     def __getattr__(self, key):
  88         if key in self._delegates:
  89             if callable(getattr(self._meta, key)):
  90                 return partial(self._function_map, key)
  91             else:
  92                 return self._property_map(key)
  93         else:
  94             raise AttributeError(key)
  95 
  96 
  97 class DatetimeAccessor(Accessor):
  98     """Accessor object for datetimelike properties of the Series values.
  99 
  100     Examples
  101     --------
  102 
  103     >>> s.dt.microsecond  # doctest: +SKIP
  104     """
  105 
  106     _accessor_name = "dt"
  107 
  108 
  109 class StringAccessor(Accessor):
  110     """Accessor object for string properties of the Series values.
  111 
  112     Examples
  113     --------
  114 
  115     >>> s.str.lower()  # doctest: +SKIP
  116     """
  117 
  118     _accessor_name = "str"
  119     _not_implemented = {"get_dummies"}
  120 
  121     @derived_from(pd.core.strings.StringMethods)
  122     def split(self, pat=None, n=-1, expand=False):
  123         if expand:
  124             if n == -1:
  125                 raise NotImplementedError(
  126                     "To use the expand parameter you must specify the number of "
  127                     "expected splits with the n= parameter. Usually n splits result in n+1 output columns."
  128                 )
  129             else:
  130                 delimiter = " " if pat is None else pat
  131                 meta = self._series._meta._constructor(
  132                     [delimiter.join(["a"] * (n + 1))],
  133                     index=self._series._meta_nonempty[:1].index,
  134                 )
  135                 meta = meta.str.split(n=n, expand=expand, pat=pat)
  136         else:
  137             meta = (self._series.name, object)
  138         return self._function_map("split", pat=pat, n=n, expand=expand, meta=meta)
  139 
  140     @derived_from(pd.core.strings.StringMethods)
  141     def cat(self, others=None, sep=None, na_rep=None):
  142         from .core import Index, Series
  143 
  144         if others is None:
  145             raise NotImplementedError("x.str.cat() with `others == None`")
  146 
  147         valid_types = (Series, Index, pd.Series, pd.Index)
  148         if isinstance(others, valid_types):
  149             others = [others]
  150         elif not all(isinstance(a, valid_types) for a in others):
  151             raise TypeError("others must be Series/Index")
  152 
  153         return self._series.map_partitions(
  154             str_cat, *others, sep=sep, na_rep=na_rep, meta=self._series._meta
  155         )
  156 
  157     @derived_from(pd.core.strings.StringMethods)
  158     def extractall(self, pat, flags=0):
  159         return self._series.map_partitions(
  160             str_extractall, pat, flags, token="str-extractall"
  161         )
  162 
  163     def __getitem__(self, index):
  164         return self._series.map_partitions(str_get, index, meta=self._series._meta)
  165 
  166 
  167 def str_extractall(series, pat, flags):
  168     return series.str.extractall(pat, flags=flags)
  169 
  170 
  171 def str_get(series, index):
  172     """ Implements series.str[index] """
  173     return series.str[index]
  174 
  175 
  176 def str_cat(self, *others, **kwargs):
  177     return self.str.cat(others=others, **kwargs)
  178
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/dask/dataframe/accessor.py b/dask/dataframe/accessor.py
  --- a/dask/dataframe/accessor.py
  +++ b/dask/dataframe/accessor.py
  @@ -142,7 +142,15 @@
           from .core import Index, Series
   
           if others is None:
  -            raise NotImplementedError("x.str.cat() with `others == None`")
  +
  +            def str_cat_none(x):
  +
  +                if isinstance(x, (Series, Index)):
  +                    x = x.compute()
  +
  +                return x.str.cat(sep=sep, na_rep=na_rep)
  +
  +            return self._series.reduction(chunk=str_cat_none, aggregate=str_cat_none)
   
           valid_types = (Series, Index, pd.Series, pd.Index)
           if isinstance(others, valid_types):
  
verification_info: {"golden_diff": "diff --git a/dask/dataframe/accessor.py b/dask/dataframe/accessor.py\n--- a/dask/dataframe/accessor.py\n+++ b/dask/dataframe/accessor.py\n@@ -142,7 +142,15 @@\n         from .core import Index, Series\n \n         if others is None:\n-            raise NotImplementedError(\"x.str.cat() with `others == None`\")\n+\n+            def str_cat_none(x):\n+\n+                if isinstance(x, (Series, Index)):\n+                    x = x.compute()\n+\n+                return x.str.cat(sep=sep, na_rep=na_rep)\n+\n+            return self._series.reduction(chunk=str_cat_none, aggregate=str_cat_none)\n \n         valid_types = (Series, Index, pd.Series, pd.Index)\n         if isinstance(others, valid_types):\n", "issue": "Note on `Add x.str.cat (#3028)` (lines 125-126)\nIt's not clear to me why `String.str.cat` isn't supported in Dask when `others == None`. Not having the ability to concat a single series into a string is a significant cost, I think. Unless there's a reason for this condition, I recommend deleting lines 126-126.\r\n\n", "before_files": [{"content": "from functools import partial\n\nimport numpy as np\nimport pandas as pd\n\nfrom ..utils import derived_from\n\n\ndef maybe_wrap_pandas(obj, x):\n    if isinstance(x, np.ndarray):\n        if isinstance(obj, pd.Series):\n            return pd.Series(x, index=obj.index, dtype=x.dtype)\n        return pd.Index(x)\n    return x\n\n\nclass Accessor:\n    \"\"\"\n    Base class for pandas Accessor objects cat, dt, and str.\n\n    Notes\n    -----\n    Subclasses should define ``_accessor_name``\n    \"\"\"\n\n    _not_implemented = set()\n\n    def __init__(self, series):\n        from .core import Series\n\n        if not isinstance(series, Series):\n            raise ValueError(\"Accessor cannot be initialized\")\n\n        series_meta = series._meta\n        if hasattr(series_meta, \"to_series\"):  # is index-like\n            series_meta = series_meta.to_series()\n        meta = getattr(series_meta, self._accessor_name)\n\n        self._meta = meta\n        self._series = series\n\n    @staticmethod\n    def _delegate_property(obj, accessor, attr):\n        out = getattr(getattr(obj, accessor, obj), attr)\n        return maybe_wrap_pandas(obj, out)\n\n    @staticmethod\n    def _delegate_method(obj, accessor, attr, args, kwargs):\n        out = getattr(getattr(obj, accessor, obj), attr)(*args, **kwargs)\n        return maybe_wrap_pandas(obj, out)\n\n    def _property_map(self, attr):\n        meta = self._delegate_property(self._series._meta, self._accessor_name, attr)\n        token = \"%s-%s\" % (self._accessor_name, attr)\n        return self._series.map_partitions(\n            self._delegate_property, self._accessor_name, attr, token=token, meta=meta\n        )\n\n    def _function_map(self, attr, *args, **kwargs):\n        if \"meta\" in kwargs:\n            meta = kwargs.pop(\"meta\")\n        else:\n            meta = self._delegate_method(\n                self._series._meta_nonempty, self._accessor_name, attr, args, kwargs\n            )\n        token = \"%s-%s\" % (self._accessor_name, attr)\n        return self._series.map_partitions(\n            self._delegate_method,\n            self._accessor_name,\n            attr,\n            args,\n            kwargs,\n            meta=meta,\n            token=token,\n        )\n\n    @property\n    def _delegates(self):\n        return set(dir(self._meta)) - self._not_implemented\n\n    def __dir__(self):\n        o = self._delegates\n        o.update(self.__dict__)\n        o.update(dir(type(self)))\n        return list(o)\n\n    def __getattr__(self, key):\n        if key in self._delegates:\n            if callable(getattr(self._meta, key)):\n                return partial(self._function_map, key)\n            else:\n                return self._property_map(key)\n        else:\n            raise AttributeError(key)\n\n\nclass DatetimeAccessor(Accessor):\n    \"\"\"Accessor object for datetimelike properties of the Series values.\n\n    Examples\n    --------\n\n    >>> s.dt.microsecond  # doctest: +SKIP\n    \"\"\"\n\n    _accessor_name = \"dt\"\n\n\nclass StringAccessor(Accessor):\n    \"\"\"Accessor object for string properties of the Series values.\n\n    Examples\n    --------\n\n    >>> s.str.lower()  # doctest: +SKIP\n    \"\"\"\n\n    _accessor_name = \"str\"\n    _not_implemented = {\"get_dummies\"}\n\n    @derived_from(pd.core.strings.StringMethods)\n    def split(self, pat=None, n=-1, expand=False):\n        if expand:\n            if n == -1:\n                raise NotImplementedError(\n                    \"To use the expand parameter you must specify the number of \"\n                    \"expected splits with the n= parameter. Usually n splits result in n+1 output columns.\"\n                )\n            else:\n                delimiter = \" \" if pat is None else pat\n                meta = self._series._meta._constructor(\n                    [delimiter.join([\"a\"] * (n + 1))],\n                    index=self._series._meta_nonempty[:1].index,\n                )\n                meta = meta.str.split(n=n, expand=expand, pat=pat)\n        else:\n            meta = (self._series.name, object)\n        return self._function_map(\"split\", pat=pat, n=n, expand=expand, meta=meta)\n\n    @derived_from(pd.core.strings.StringMethods)\n    def cat(self, others=None, sep=None, na_rep=None):\n        from .core import Index, Series\n\n        if others is None:\n            raise NotImplementedError(\"x.str.cat() with `others == None`\")\n\n        valid_types = (Series, Index, pd.Series, pd.Index)\n        if isinstance(others, valid_types):\n            others = [others]\n        elif not all(isinstance(a, valid_types) for a in others):\n            raise TypeError(\"others must be Series/Index\")\n\n        return self._series.map_partitions(\n            str_cat, *others, sep=sep, na_rep=na_rep, meta=self._series._meta\n        )\n\n    @derived_from(pd.core.strings.StringMethods)\n    def extractall(self, pat, flags=0):\n        return self._series.map_partitions(\n            str_extractall, pat, flags, token=\"str-extractall\"\n        )\n\n    def __getitem__(self, index):\n        return self._series.map_partitions(str_get, index, meta=self._series._meta)\n\n\ndef str_extractall(series, pat, flags):\n    return series.str.extractall(pat, flags=flags)\n\n\ndef str_get(series, index):\n    \"\"\" Implements series.str[index] \"\"\"\n    return series.str[index]\n\n\ndef str_cat(self, *others, **kwargs):\n    return self.str.cat(others=others, **kwargs)\n", "path": "dask/dataframe/accessor.py"}], "after_files": [{"content": "from functools import partial\n\nimport numpy as np\nimport pandas as pd\n\nfrom ..utils import derived_from\n\n\ndef maybe_wrap_pandas(obj, x):\n    if isinstance(x, np.ndarray):\n        if isinstance(obj, pd.Series):\n            return pd.Series(x, index=obj.index, dtype=x.dtype)\n        return pd.Index(x)\n    return x\n\n\nclass Accessor:\n    \"\"\"\n    Base class for pandas Accessor objects cat, dt, and str.\n\n    Notes\n    -----\n    Subclasses should define ``_accessor_name``\n    \"\"\"\n\n    _not_implemented = set()\n\n    def __init__(self, series):\n        from .core import Series\n\n        if not isinstance(series, Series):\n            raise ValueError(\"Accessor cannot be initialized\")\n\n        series_meta = series._meta\n        if hasattr(series_meta, \"to_series\"):  # is index-like\n            series_meta = series_meta.to_series()\n        meta = getattr(series_meta, self._accessor_name)\n\n        self._meta = meta\n        self._series = series\n\n    @staticmethod\n    def _delegate_property(obj, accessor, attr):\n        out = getattr(getattr(obj, accessor, obj), attr)\n        return maybe_wrap_pandas(obj, out)\n\n    @staticmethod\n    def _delegate_method(obj, accessor, attr, args, kwargs):\n        out = getattr(getattr(obj, accessor, obj), attr)(*args, **kwargs)\n        return maybe_wrap_pandas(obj, out)\n\n    def _property_map(self, attr):\n        meta = self._delegate_property(self._series._meta, self._accessor_name, attr)\n        token = \"%s-%s\" % (self._accessor_name, attr)\n        return self._series.map_partitions(\n            self._delegate_property, self._accessor_name, attr, token=token, meta=meta\n        )\n\n    def _function_map(self, attr, *args, **kwargs):\n        if \"meta\" in kwargs:\n            meta = kwargs.pop(\"meta\")\n        else:\n            meta = self._delegate_method(\n                self._series._meta_nonempty, self._accessor_name, attr, args, kwargs\n            )\n        token = \"%s-%s\" % (self._accessor_name, attr)\n        return self._series.map_partitions(\n            self._delegate_method,\n            self._accessor_name,\n            attr,\n            args,\n            kwargs,\n            meta=meta,\n            token=token,\n        )\n\n    @property\n    def _delegates(self):\n        return set(dir(self._meta)) - self._not_implemented\n\n    def __dir__(self):\n        o = self._delegates\n        o.update(self.__dict__)\n        o.update(dir(type(self)))\n        return list(o)\n\n    def __getattr__(self, key):\n        if key in self._delegates:\n            if callable(getattr(self._meta, key)):\n                return partial(self._function_map, key)\n            else:\n                return self._property_map(key)\n        else:\n            raise AttributeError(key)\n\n\nclass DatetimeAccessor(Accessor):\n    \"\"\"Accessor object for datetimelike properties of the Series values.\n\n    Examples\n    --------\n\n    >>> s.dt.microsecond  # doctest: +SKIP\n    \"\"\"\n\n    _accessor_name = \"dt\"\n\n\nclass StringAccessor(Accessor):\n    \"\"\"Accessor object for string properties of the Series values.\n\n    Examples\n    --------\n\n    >>> s.str.lower()  # doctest: +SKIP\n    \"\"\"\n\n    _accessor_name = \"str\"\n    _not_implemented = {\"get_dummies\"}\n\n    @derived_from(pd.core.strings.StringMethods)\n    def split(self, pat=None, n=-1, expand=False):\n        if expand:\n            if n == -1:\n                raise NotImplementedError(\n                    \"To use the expand parameter you must specify the number of \"\n                    \"expected splits with the n= parameter. Usually n splits result in n+1 output columns.\"\n                )\n            else:\n                delimiter = \" \" if pat is None else pat\n                meta = self._series._meta._constructor(\n                    [delimiter.join([\"a\"] * (n + 1))],\n                    index=self._series._meta_nonempty[:1].index,\n                )\n                meta = meta.str.split(n=n, expand=expand, pat=pat)\n        else:\n            meta = (self._series.name, object)\n        return self._function_map(\"split\", pat=pat, n=n, expand=expand, meta=meta)\n\n    @derived_from(pd.core.strings.StringMethods)\n    def cat(self, others=None, sep=None, na_rep=None):\n        from .core import Index, Series\n\n        if others is None:\n\n            def str_cat_none(x):\n\n                if isinstance(x, (Series, Index)):\n                    x = x.compute()\n\n                return x.str.cat(sep=sep, na_rep=na_rep)\n\n            return self._series.reduction(chunk=str_cat_none, aggregate=str_cat_none)\n\n        valid_types = (Series, Index, pd.Series, pd.Index)\n        if isinstance(others, valid_types):\n            others = [others]\n        elif not all(isinstance(a, valid_types) for a in others):\n            raise TypeError(\"others must be Series/Index\")\n\n        return self._series.map_partitions(\n            str_cat, *others, sep=sep, na_rep=na_rep, meta=self._series._meta\n        )\n\n    @derived_from(pd.core.strings.StringMethods)\n    def extractall(self, pat, flags=0):\n        return self._series.map_partitions(\n            str_extractall, pat, flags, token=\"str-extractall\"\n        )\n\n    def __getitem__(self, index):\n        return self._series.map_partitions(str_get, index, meta=self._series._meta)\n\n\ndef str_extractall(series, pat, flags):\n    return series.str.extractall(pat, flags=flags)\n\n\ndef str_get(series, index):\n    \"\"\" Implements series.str[index] \"\"\"\n    return series.str[index]\n\n\ndef str_cat(self, *others, **kwargs):\n    return self.str.cat(others=others, **kwargs)\n", "path": "dask/dataframe/accessor.py"}]}