At 16:50 in this video, the teacher says that if all examples come to one side, the info gain is minus inf. But according to the formula for info gain, it should be 0 in this case as entropy before and after split will be equal.
Information Gain
Yes you can return 0 as well, sir said information gain will be minimum, so to highlight this fact, we returned -1000000, and no other reason.
Hope this helped you.