Add new comment is 0 for some Canon cameras

For my astro image calibration program I wish to use the value but I have noticed for the Canon T5i and T7i this parameter is zero. For my Nikon D5300 the value is 600 which I believe is correct. I believe that for these Canon cameras the black level should be in the 2,000 to 3,000 range. Is there a better way to determine the correct black level?