seabornのfactorplotやbarplotでエラーが出る。

sns.factorplot(x="給与/交通費　備考", y="応募数 合計", data=train, kind='bar')

を実行すると以下のようなエラーが出てきます。

TypeError                                 Traceback (most recent call last)
<ipython-input-115-b38d4545c9af> in <module>()
----> 1 sns.factorplot(x="給与/交通費　備考", y="応募数 合計", data=train, kind='bar')

~\Anaconda3\lib\site-packages\seaborn\categorical.py in factorplot(x, y, hue, data, row, col, col_wrap, estimator, ci, n_boot, units, order, hue_order, row_order, col_order, kind, size, aspect, orient, color, palette, legend, legend_out, sharex, sharey, margin_titles, facet_kws, **kwargs)
   3489     # facets to ensure representation of all data in the final plot
   3490     p = _CategoricalPlotter()
-> 3491     p.establish_variables(x_, y_, hue, data, orient, order, hue_order)
   3492     order = p.group_names
   3493     hue_order = p.hue_names

~\Anaconda3\lib\site-packages\seaborn\categorical.py in establish_variables(self, x, y, hue, data, orient, order, hue_order, units)
    142                 x = data.get(x, x)
    143                 y = data.get(y, y)
--> 144                 hue = data.get(hue, hue)
    145                 units = data.get(units, units)
    146 

~\Anaconda3\lib\site-packages\pandas\core\generic.py in get(self, key, default)
   2472         """
   2473         try:
-> 2474             return self[key]
   2475         except (KeyError, ValueError, IndexError):
   2476             return default

~\Anaconda3\lib\site-packages\pandas\core\frame.py in __getitem__(self, key)
   2683             return self._getitem_multilevel(key)
   2684         else:
-> 2685             return self._getitem_column(key)
   2686 
   2687     def _getitem_column(self, key):

~\Anaconda3\lib\site-packages\pandas\core\frame.py in _getitem_column(self, key)
   2693 
   2694         # duplicate columns & possible reduce dimensionality
-> 2695         result = self._constructor(self._data.get(key))
   2696         if result.columns.is_unique:
   2697             result = result[key]

~\Anaconda3\lib\site-packages\pandas\core\internals.py in get(self, item, fastpath)
   4128 
   4129             if isna(item):
-> 4130                 raise TypeError("cannot label index with a null key")
   4131 
   4132             indexer = self.items.get_indexer_for([item])

TypeError: cannot label index with a null key

調べたところ、同じカラムが二つあったりすると出るエラーみたいですが、見当たりませんでした。
なにか心当たりがある方がいたら教えていただきたいです。