In pandas 0.22 series changes behavior of mode method. This is a fix to mantain the same behavior in categorical imputer

Author: arielrossanigo

sklearn_pandas/categorical_imputer.py

@@ -100,6 +100,8 @@ def fit(self, X, y=None):
         elif self.strategy == 'fixed_value':
             modes = np.array([self.replacement])
         if modes.shape[0] == 0:
+            raise ValueError('Data is empty or all values are null')
+        elif modes.shape[0] > 1:
             raise ValueError('No value is repeated more than '
                              'once in the column')
         else: