Hey, this doesn't make any difference - that is include zero values, not include null values. e.g. this is my graph with or without the "include null values" button ticked.
This is the chart when converted to a bar chart - you can see the huge null value column on the preview at the bottom which is messing up the scale, far right:
This is the bar chart when you untick the "include null value" option which is available under the dimension in the bar chart field, you get this:
Which then you can convert to a line chart. Unticking the "include zero values" box just removes the first two days on this bar chart.
Final line chart:
I'm using 3.2 SR4, and the documentation for the line chart says it's supposed to be there under the dimension properties!
I could use a set expression, but in this case I am far more likely to just save it as a master visualisation. However, if this is supposed to be a self-service platform for business users, I really don't expect them to have to go through all these steps or write set expressions - it looks like a bug to me.