Running total with blank month

I have an incident table that has a date field , the issue I am facing is there can be insitances where there is no incidents for the month resulting in blank dates so I created a calendar table and setup a one to many relatioship to my incident table on the Date>IncidentDate fields.

My reqriment is to create a running total for the incidents on a month to month basis and if there is a blank month return the previous months incident total 


for some reason I cant accomplish this without A skipping over May resulting in a break in my line visual or a continous past the current month causing confusion as why we have incidents in months that didnt happen yet 

Any help would be appreciated!