fix: presentation with empty credential fix (#3319)

This change fixes how a presentation is marshalled with empty credential field which wrongly outputs:
'"verifiableCredential": null'

This change skips this field if the presentation Credential field is empty

Signed-off-by: Baha Shaaban <baha.shaaban@securekey.com>

pkg/doc/verifiable/presentation.go

@@ -286,17 +286,22 @@ func (vp *Presentation) raw() (*rawPresentation, error) {
 		return nil, err
 	}
 
-	return &rawPresentation{
+	rp := &rawPresentation{
 		// TODO single value contexts should be compacted as part of Issue [#1730]
 		// Not compacting now to support interoperability
 		Context:      vp.Context,
 		ID:           vp.ID,
 		Type:         typesToRaw(vp.Type),
-		Credential:   vp.credentials,
 		Holder:       vp.Holder,
 		Proof:        proof,
 		CustomFields: vp.CustomFields,
-	}, nil
+	}
+
+	if len(vp.credentials) > 0 {
+		rp.Credential = vp.credentials
+	}
+
+	return rp, nil
 }
 
 // rawPresentation is a basic verifiable credential.

pkg/doc/verifiable/presentation_test.go

@@ -54,6 +54,19 @@ const validPresentation = `
 }
 `
 
+const presentationWithoutCredentials = `
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1",
+    "https://www.w3.org/2018/credentials/examples/v1",
+    "https://trustbloc.github.io/context/vc/examples-v1.jsonld"
+  ],
+  "id": "urn:uuid:3978344f-8596-4c3a-a978-8fcaba3903c5",
+  "type": "VerifiablePresentation",
+  "holder": "did:example:ebfeb1f712ebc6f1c276e12ec21"
+}
+`
+
 const validPresentationWithCustomFields = `
 {
   "@context": [
@@ -130,6 +143,38 @@ func TestParsePresentation(t *testing.T) {
 		require.Equal(t, "did:example:ebfeb1f712ebc6f1c276e12ec21", vp.Holder)
 	})
 
+	t.Run("creates a new Verifiable Presentation from valid JSON without credentials", func(t *testing.T) {
+		vp, err := newTestPresentation(t, []byte(presentationWithoutCredentials), WithPresStrictValidation())
+		require.NoError(t, err)
+		require.NotNil(t, vp)
+
+		// validate @context
+		require.Equal(t, []string{
+			"https://www.w3.org/2018/credentials/v1",
+			"https://www.w3.org/2018/credentials/examples/v1",
+			"https://trustbloc.github.io/context/vc/examples-v1.jsonld",
+		}, vp.Context)
+
+		// check id
+		require.Equal(t, "urn:uuid:3978344f-8596-4c3a-a978-8fcaba3903c5", vp.ID)
+
+		// check type
+		require.Equal(t, []string{"VerifiablePresentation"}, vp.Type)
+
+		// check verifiableCredentials
+		require.Nil(t, vp.Credentials())
+		require.Empty(t, vp.Credentials())
+
+		// check holder
+		require.Equal(t, "did:example:ebfeb1f712ebc6f1c276e12ec21", vp.Holder)
+
+		// check rawPresentation
+		rp, err := vp.raw()
+		require.NoError(t, err)
+
+		require.IsType(t, nil, rp.Credential)
+	})
+
 	t.Run("creates a new Verifiable Presentation with custom/additional fields", func(t *testing.T) {
 		verify := func(t *testing.T, vp *Presentation) {
 			require.Len(t, vp.CustomFields, 1)