Graph has no Continuous Trend Line
Smartsheet has great visual graphs, one problem however is it does not have continuous trendlines (like Excel  but this isn't perfect either). So If I have 12 months and say 4 data points, I end up with a partline & scatter plot; instead of the line graph I selected (does not show the full line or full trend).
Ideally I would have 3 line graph suboptions:
1. Include 0 / null values in line [eg line goes to zero for each 0 / null value]
2. Exclude 0/ null values  no line [eg reverts to scatter graph]
3. Exclude 0/null values  with line [eg line ignores 0 value, going direct from say '4' in Apr to '4.5 ' in Sep]
Answers

So the issues for your 3 options are different so I'll respond to each one separately.
 The issue you have is that some categories only has a value let's say in May but not in the proceeding or following month so it can't do a line, but rather a dot. You'll need to include values or a formula to calculate values so that every single month has a value, even a zero so that it can connect the dots. Point, you can't have a null value, it must be a numeric of some value or it will not have a line/dot.
 You can't plot just dots in a line graph. The only reason you have dots now is because there's no previous or following value so it only does the dot, if it has a value in two consecutive months, it will do a line. If you want scatter you'll have to use a scatter type chart.
 In this case you'd have to write a formula that said something to the effect of: If( XYZ = 0, then use the previous month's value, otherwise, XYZ).
Simply this is a line graph and lines are a game of connect the dot. If you don't have a consecutive value it will only do a dot or the start of the next line where consecutives exist. Alternatively you can't make it only do dots if you have consecutive values, because it's a line graph. Lastly if you want lines or dots to exists where they cannot (due to no value), you have to via formula a create a logically calculated value.

(in case anyone else has this issue) My solution is to move the data to Google Sheets which provides the common sense function required:
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