Sorry Kevin (I upvoted 1 answer and downvoted another 5 for a net rep change of 0). I was unable to use Data.SE1 to find user/date combinations netting a non-0-vote, 0-rep day.
The image fails to register a bar for the day Mar 29, where Kevin in fact had 6 rep changes. This test case has the day at the end of the graph, so maybe there's code to end the graph on the "last day in range with non-zero rep change". My real goal was to see if the missing 0-height green bar will cause the day to be unclickable. A 2-rep change (acceptance) still draws a sliver of a bar.