Tell if no automatic update possible

tools/update_whatsnew.py

@@ -6,7 +6,7 b' whatsnew/development.rst (chronologically ordered), and deletes the snippets.'
 """
 
 import io
-import os
+import sys
 from glob import glob
 from os.path import dirname, basename, abspath, join as pjoin
 from subprocess import check_call, check_output
@@ -28,6 +28,10 b' files.difference_update({pjoin(pr_dir, f) for f in {'
                          'antigravity-feature.rst'}
                          })
 
+if not files:
+    print("No automatic update available for what's new")
+    sys.exit(0)
+
 
 def getmtime(f):
     return check_output(['git', 'log', '-1', '--format="%ai"', '--', f])