Fix a coding error that was introduced in 26423.

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index 902d8e84669441caa13da52c2c31637f337d53f3..148855c89ffc597d645314df55274da19909f303 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -51,8 +51,8 @@ class SCMWrapper(object):
 
   def RunCommand(self, command, options, args, file_list=None):
     # file_list will have all files that are modified appended to it.
-
-    file_list = file_list or []
+    if file_list is None:
+      file_list = []
 
     commands = {
       'cleanup':  self.cleanup,