no differences reported for maps where values are empty structs

[aexvir]

in a case where there is a type defined such as

type Set map[string]struct{}

the result of diffing these types always ends up with an empty changelog, even if there are differences on the keys

after digging a bit through the codebase I've realized that the structValues method won't add any entry to the changelog if the struct has no fields; when diffing maps, for a specific key, if any of the maps doesn't have a value for that key, there is a shortcut that simply returns the output of structValues as either create or delete depending which map is missing the data

this, effectively makes the changelog to be empty for the following case

a := Set{"existing": struct{}}
b := Set{}