blender-thumbnailer.py needs two arguments <input.blend> and <output.png>, so if calling it with no argument, it shows error message as:

$ release/bin/blender-thumbnailer.py
Expected 2 arguments <input.blend> <output.png>
$

I noticed, however, it doesn't show the error message if only one argument is given.

Please modify it like below:

--- blender/release/bin/blender-thumbnailer.py (revision 34646)
+++ blender/release/bin/blender-thumbnailer.py (working copy)
@@ -118,7 +118,7 @@
if __name__ == '__main__':
import sys

- if len(sys.argv) < 2:
+ if len(sys.argv) < 3:
print("Expected 2 arguments <input.blend> <output.png>")
else:
file_in = sys.argv[-2]