diff --git a/comid/integrityregisters.go b/comid/integrityregisters.go
index e8df59f3..9a40850e 100644
--- a/comid/integrityregisters.go
+++ b/comid/integrityregisters.go
@@ -13,6 +13,7 @@ import (
 const TextType = "text"
 
 // IRegisterIndex is the interface to hold register index
+// Supported index types are uint and text
 type IRegisterIndex interface{}
 
 // IntegrityRegisters holds the Integrity Registers
@@ -24,7 +25,8 @@ func NewIntegrityRegisters() *IntegrityRegisters {
 	return &IntegrityRegisters{m: make(map[IRegisterIndex]Digests)}
 }
 
-// AddDigests allows inserting a series of Digests at a specific RegisterIndex
+// AddDigests allows inserting an array of digests at a specific index
+// Supported index types are uint and text
 func (i *IntegrityRegisters) AddDigests(index IRegisterIndex, digests Digests) error {
 	if len(digests) == 0 {
 		return fmt.Errorf("no digests to add")
@@ -37,9 +39,9 @@ func (i *IntegrityRegisters) AddDigests(index IRegisterIndex, digests Digests) e
 	return nil
 }
 
-// AddDigest allows inserting a Digest at a specific registerIndex
+// AddDigest allows inserting a digest at a specific index
+// Supported index types are uint and text
 func (i *IntegrityRegisters) AddDigest(index IRegisterIndex, digest swid.HashEntry) error {
-
 	if i.m == nil {
 		return fmt.Errorf("no register to add digest")
 	}
@@ -96,6 +98,9 @@ func (i IntegrityRegisters) MarshalJSON() ([]byte, error) {
 }
 
 func (i *IntegrityRegisters) UnmarshalJSON(data []byte) error {
+	if i.m == nil {
+		i.m = make(map[IRegisterIndex]Digests)
+	}
 	jmap := make(map[string]json.RawMessage)
 	var index IRegisterIndex
 	if err := json.Unmarshal(data, &jmap); err != nil {
diff --git a/comid/integrityregisters_test.go b/comid/integrityregisters_test.go
index 38e79260..a914e287 100644
--- a/comid/integrityregisters_test.go
+++ b/comid/integrityregisters_test.go
@@ -152,7 +152,6 @@ func TestIntegrityRegisters_MarshalCBOR_TextIndex_OK(t *testing.T) {
 }
 
 func TestIntegrityRegisters_UnmarshalCBOR_TextIndex_OK(t *testing.T) {
-
 	expected := IntegrityRegisters{map[IRegisterIndex]Digests{
 		"0": []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		"1": []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
@@ -211,10 +210,10 @@ func TestIntegrityRegisters_MarshalJSON_TextIndex_OK(t *testing.T) {
 
 func TestIntegrityRegisters_UnmarshalJSON_TextIndex_OK(t *testing.T) {
 	j := `{"abcd":{"key_type":"text","Value":["sha-256;5Fty9cDAtXLbTY06t+l/No/3TmI0eoJN7LZ6hOUiTXU="]}}`
-	expected := &IntegrityRegisters{map[IRegisterIndex]Digests{
+	expected := IntegrityRegisters{map[IRegisterIndex]Digests{
 		"abcd": []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 	}}
-	actual := NewIntegrityRegisters()
+	actual := IntegrityRegisters{}
 	err := actual.UnmarshalJSON([]byte(j))
 	require.NoError(t, err)
 	require.True(t, reflect.DeepEqual(expected, actual))
@@ -228,14 +227,14 @@ func TestIntegrityRegisters_UnmarshalJSON_UIntIndex_OK(t *testing.T) {
 	"3":{"key_type":"uint","Value":["sha-256;5Fty9cDAtXLbTY06t+l/No/3TmI0eoJN7LZ6hOUiTXU="]},
 	"4":{"key_type":"uint","Value":["sha-256;5Fty9cDAtXLbTY06t+l/No/3TmI0eoJN7LZ6hOUiTXU="]}
 	}`
-	expected := &IntegrityRegisters{map[IRegisterIndex]Digests{
+	expected := IntegrityRegisters{map[IRegisterIndex]Digests{
 		uint(0): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		uint(1): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		uint(2): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		uint(3): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		uint(4): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 	}}
-	actual := NewIntegrityRegisters()
+	actual := IntegrityRegisters{}
 	err := actual.UnmarshalJSON([]byte(j))
 	require.NoError(t, err)
 	require.True(t, reflect.DeepEqual(expected, actual))
@@ -249,7 +248,7 @@ func TestIntegrityRegisters_UnmarshalJSON_TextUInt_Index_OK(t *testing.T) {
 		"3":{"key_type":"text","Value":["sha-256;5Fty9cDAtXLbTY06t+l/No/3TmI0eoJN7LZ6hOUiTXU="]},
 		"4":{"key_type":"text","Value":["sha-256;5Fty9cDAtXLbTY06t+l/No/3TmI0eoJN7LZ6hOUiTXU="]}
 		}`
-	expected := &IntegrityRegisters{
+	expected := IntegrityRegisters{
 		map[IRegisterIndex]Digests{
 			uint(0): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 			uint(1): []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
@@ -257,7 +256,7 @@ func TestIntegrityRegisters_UnmarshalJSON_TextUInt_Index_OK(t *testing.T) {
 			"3":     []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 			"4":     []swid.HashEntry{{HashAlgID: swid.Sha256, HashValue: MustHexDecode(t, "e45b72f5c0c0b572db4d8d3ab7e97f368ff74e62347a824decb67a84e5224d75")}},
 		}}
-	actual := NewIntegrityRegisters()
+	actual := IntegrityRegisters{}
 	err := actual.UnmarshalJSON([]byte(j))
 	require.NoError(t, err)
 	require.True(t, reflect.DeepEqual(expected, actual))
@@ -291,7 +290,7 @@ func TestIntegrityRegisters_UnmarshalJSON_NOK(t *testing.T) {
 		},
 	} {
 		t.Run(tv.Name, func(t *testing.T) {
-			reg := NewIntegrityRegisters()
+			reg := IntegrityRegisters{}
 			err := reg.UnmarshalJSON([]byte(tv.Input))
 			assert.EqualError(t, err, tv.Err)
 		})