use zero value for nils in ID generation

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/formats/syftjson/test-fixtures/snapshot/TestDirectoryPresenter.golden

@@ -1,7 +1,7 @@
 {
  "artifacts": [
   {
-   "id": "810333194629225077",
+   "id": "14696638697550896878",
    "name": "package-1",
    "version": "1.0.1",
    "type": "python",

syft/pkg/package.go

@@ -19,7 +19,6 @@ type Package struct {
 	Version      string            // the version of the package
 	FoundBy      string            // the specific cataloger that discovered this package
 	Locations    []source.Location // the locations that lead to the discovery of this package (note: this is not necessarily the locations that make up this package)
-	// TODO: should we move licenses into metadata?
 	Licenses     []string          // licenses discovered with the package metadata
 	Language     Language          // the language ecosystem this package belongs to (e.g. JavaScript, Python, etc)
 	Type         Type              // the package type (e.g. Npm, Yarn, Python, Rpm, Deb, etc)
@@ -47,7 +46,7 @@ func (p Package) String() string {
 
 func (p Package) Fingerprint() (string, error) {
 	f, err := hashstructure.Hash(p, hashstructure.FormatV2, &hashstructure.HashOptions{
-		//ZeroNil:      true,
+		ZeroNil:      true,
 		SlicesAsSets: true,
 	})
 	if err != nil {