Make CheckLicense() to not trigger on empty files.

tests/presubmit_unittest.py

 #!/usr/bin/python
 # Copyright (c) 2010 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Unit tests for presubmit_support.py and presubmit_canned_checks.py."""
 
 import StringIO
 
 # Fixes include path.
@@ skipping 1368 matching lines @@
     # Test CheckSvnProperty at the same time.
     self.SvnPropertyTest(presubmit_canned_checks.CheckChangeSvnEolStyle,
                          'svn:eol-style', 'LF', '', True,
                          presubmit.OutputApi.PresubmitError, True)
 
   def testCheckChangeSvnEolStyleUpload(self):
     self.SvnPropertyTest(presubmit_canned_checks.CheckChangeSvnEolStyle,
                          'svn:eol-style', 'LF', '', False,
                          presubmit.OutputApi.PresubmitNotifyResult, True)
 
-  def _LicenseCheck(self, text, license, committing, expected_result):
+  def _LicenseCheck(self, text, license, committing, expected_result, **kwargs):
     change = self.mox.CreateMock(presubmit.SvnChange)
     change.scm = 'svn'
     input_api = self.MockInputApi(change, committing)
     affected_file = self.mox.CreateMock(presubmit.SvnAffectedFile)
     input_api.AffectedSourceFiles(42).AndReturn([affected_file])
     input_api.ReadFile(affected_file, 'rb').AndReturn(text)
     if expected_result:
       affected_file.LocalPath().AndReturn('bleh')
 
     self.mox.ReplayAll()
     result = presubmit_canned_checks.CheckLicense(
-                 input_api, presubmit.OutputApi, license, 42)
+                 input_api, presubmit.OutputApi, license, source_file_filter=42,
+                 **kwargs)
     if expected_result:
       self.assertEqual(len(result), 1)
       self.assertEqual(result[0].__class__, expected_result)
     else:
       self.assertEqual(result, [])
 
   def testCheckLicenseSuccess(self):
     text = (
         "#!/bin/python\n"
         "# Copyright (c) 2037 Nobody.\n"
@@ skipping 27 matching lines @@
         "# All Rights Reserved.\n"
         "print 'foo'\n"
     )
     license = (
         r".*? Copyright \(c\) 0007 Nobody." "\n"
         r".*? All Rights Reserved\." "\n"
     )
     self._LicenseCheck(text, license, False,
                        presubmit.OutputApi.PresubmitNotifyResult)
 
+  def testCheckLicenseEmptySuccess(self):
+    text = ''
+    license = (
+        r".*? Copyright \(c\) 2037 Nobody." "\n"
+        r".*? All Rights Reserved\." "\n"
+    )
+    self._LicenseCheck(text, license, True, None, accept_empty_files=True)
+
   def testCannedCheckSvnAccidentalSubmission(self):
     modified_dir_file = 'foo/'
     accidental_submssion_file = 'foo/bar.cc'
 
     change = self.mox.CreateMock(presubmit.SvnChange)
     change.scm = 'svn'
     change.GetModifiedFiles().AndReturn([modified_dir_file])
     change.GetAllModifiedFiles().AndReturn([modified_dir_file,
                                             accidental_submssion_file])
     input_api = self.MockInputApi(change, True)
@@ skipping 280 matching lines @@
     results = presubmit_canned_checks.CheckBuildbotPendingBuilds(
         input_api, presubmit.OutputApi, 'uurl', 2, ('foo'))
     self.assertEquals(len(results), 1)
     self.assertEquals(results[0].__class__,
         presubmit.OutputApi.PresubmitNotifyResult)
 
 
 if __name__ == '__main__':
   import unittest
   unittest.main()