fix empty history crash

tests/test_types.py

@@ -139,6 +139,7 @@ class TestCommand(object):
                                       env=os_environ)
 
     @pytest.mark.parametrize('script, result', [
+        ([], None),
         ([''], None),
         (['', ''], None),
         (['ls', '-la'], 'ls -la'),

thefuck/entrypoints/fix_command.py

@@ -23,6 +23,7 @@ def _get_raw_command(known_args):
             diff = SequenceMatcher(a=alias, b=command).ratio()
             if diff < const.DIFF_WITH_ALIAS or command in executables:
                 return [command]
+    return []
 
 
 def fix_command(known_args):