[backport iron] ROS 2: Fixing thrown Exception in camerachecker.py (#871

) (#888)

backport ##871

Signed-off-by: Alejandro Hernández Cordero <ahcorde@gmail.com>

camera_calibration/src/camera_calibration/camera_checker.py

@@ -150,7 +150,7 @@ def image_corners(self, im):
  if ok:
  return corners, ids
  else:
- return None
+ return None, None
 
  def handle_monocular(self, msg):