What is the default numeric type for stateflow charts with the action language set to C?

Model Advisor (R2017b & 2018a) flags this stateflow chart transition with mathworks.iec61508.hisf_0015

The message is: The following expressions consist of variables and parameters of different datatypes. Expression: var1>0.0

This message occurs whether var1 is a single or double.

So, 0.0 is neither a double or single? What type is it?

I can eliminate the warning by setting the Action Language to MATLAB or type casting the numeric value "var1>double(0.0)" ... but it seems hisf_0015 is complaining about an actual type mismatch rather than the fact that 0.0 is not explicitly typed...