Don't use null for undefined properties

[caspervonb]

Saw the output of #18 and started digging around a little bit, I'm seeing null being used for a lot of optional parameters.

For example, subtypes are marked as null in https://github.com/Microsoft/edge-diagnostics-adapter/blob/master/EdgeWebKitImpl/debugger.ts#L320-L323

If there is no subtype, then the property should just not be set?

[caspervonb]

Lazy fix, change https://github.com/Microsoft/edge-diagnostics-adapter/blob/master/EdgeWebKitImpl/debugger.ts#L353 to be

if (subType) {
 /* ...*/
}

[andysterland]

@caspervonb thanks! I'll look at fixing this soon.