Fix test; trigger postcommits

Author: Abacn

.github/trigger_files/beam_PostCommit_Python.json

@@ -1,5 +1,5 @@
 {
   "comment": "Modify this file in a trivial way to cause this test suite to run.",
-  "modification": 32
+  "modification": 0
 }
 

.github/trigger_files/beam_PostCommit_Python_Xlang_Gcp_Dataflow.json

@@ -1,4 +1,4 @@
 {
   "comment": "Modify this file in a trivial way to cause this test suite to run",
-  "modification": 14
+  "modification": 0
 }

.github/trigger_files/beam_PostCommit_Python_Xlang_IO_Dataflow.json

@@ -1,4 +1,4 @@
 {
   "comment": "Modify this file in a trivial way to cause this test suite to run",
-  "modification": 5
+  "modification": 0
 }

sdks/python/apache_beam/options/pipeline_options.py

@@ -1682,6 +1682,7 @@ def _add_argparse_args(cls, parser):
             '(not __main__) and the modules are importable in the worker. '))
     parser.add_argument(
         '--disable_save_main_session',
+        default=None,
         action='store_false',
         dest='save_main_session',
         help=(