Put module import on top of the module.

transformers/pipelines.py

@@ -20,6 +20,7 @@ import os
 from abc import ABC, abstractmethod
 from contextlib import contextmanager
 from itertools import groupby
+from os.path import abspath, exists
 from typing import Union, Optional, Tuple, List, Dict
 
 import numpy as np
@@ -100,7 +101,7 @@ class PipelineDataFormat:
         if self.is_multi_columns:
             self.column = [tuple(c.split('=')) if '=' in c else (c, c) for c in self.column]
 
-        from os.path import abspath, exists
+        if output is not None:
             if exists(abspath(self.output)):
                 raise OSError('{} already exists on disk'.format(self.output))