diff --git a/swh/core/utils.py b/swh/core/utils.py
index 235d704..a4921d0 100644
--- a/swh/core/utils.py
+++ b/swh/core/utils.py
@@ -1,95 +1,96 @@
 # Copyright (C) 2016  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import os
 import itertools
 import codecs
 
 from contextlib import contextmanager
 
 
 @contextmanager
 def cwd(path):
     """Contextually change the working directory to do thy bidding.
     Then gets back to the original location.
 
     """
     prev_cwd = os.getcwd()
     os.chdir(path)
     try:
         yield
     finally:
         os.chdir(prev_cwd)
 
 
 def grouper(iterable, n):
     """Collect data into fixed-length chunks or blocks.
 
     Args:
         iterable: an iterable
         n: size of block
         fillvalue: value to use for the last block
 
     Returns:
         fixed-length chunks of blocks as iterables
 
     """
     args = [iter(iterable)] * n
     for _data in itertools.zip_longest(*args, fillvalue=None):
         yield (d for d in _data if d is not None)
 
 
 def backslashescape_errors(exception):
     if isinstance(exception, UnicodeDecodeError):
         bad_data = exception.object[exception.start:exception.end]
         escaped = ''.join(r'\x%02x' % x for x in bad_data)
         return escaped, exception.end
 
     return codecs.backslashreplace_errors(exception)
 
+
 codecs.register_error('backslashescape', backslashescape_errors)
 
 
 def encode_with_unescape(value):
     """Encode an unicode string containing \\x<hex> backslash escapes"""
     slices = []
     start = 0
     odd_backslashes = False
     i = 0
     while i < len(value):
         if value[i] == '\\':
             odd_backslashes = not odd_backslashes
         else:
             if odd_backslashes:
                 if value[i] != 'x':
                     raise ValueError('invalid escape for %r at position %d' %
                                      (value, i-1))
                 slices.append(
                     value[start:i-1].replace('\\\\', '\\').encode('utf-8')
                 )
                 slices.append(bytes.fromhex(value[i+1:i+3]))
 
                 odd_backslashes = False
                 start = i = i + 3
                 continue
 
         i += 1
 
     slices.append(
         value[start:i].replace('\\\\', '\\').encode('utf-8')
     )
 
     return b''.join(slices)
 
 
 def decode_with_escape(value):
     """Decode a bytestring as utf-8, escaping the bytes of invalid utf-8 sequences
     as \\x<hex value>. We also escape NUL bytes as they are invalid in JSON
     strings.
     """
     # escape backslashes
     value = value.replace(b'\\', b'\\\\')
     value = value.replace(b'\x00', b'\\x00')
     return value.decode('utf-8', 'backslashescape')