NonNil takes a pointer to a Go data structure (currently only a slice or a map) and makes sure it's non-nil for JSON serialization.

NonNilMapForJSON makes sure that *slicePtr is non-nil so it will won't be omitted from JSON serialization and possibly confuse JavaScript clients expecting it to be present.

NonNilSliceForJSON makes sure that *slicePtr is non-nil so it will won't be omitted from JSON serialization and possibly confuse JavaScript clients expecting it to be present.

Set populates an entry in a map, making the map if necessary.