Initialize Siblings to avoid null on json marshal

Initialize Siblings to avoid null on json marshal of empty siblings

merkletree.go

@@ -459,7 +459,7 @@ func (mt *MerkleTree) Get(k *big.Int) (*big.Int, *big.Int, []*Hash, error) {
 	path := getPath(mt.maxLevels, kHash[:])
 
 	nextKey := mt.rootKey
-	var siblings []*Hash
+	siblings := []*Hash{}
 	for i := 0; i < mt.maxLevels; i++ {
 		n, err := mt.GetNode(nextKey)
 		if err != nil {
@@ -524,7 +524,7 @@ func (mt *MerkleTree) Update(k, v *big.Int) (*CircomProcessorProof, error) {
 	cp.NewValue = vHash
 
 	nextKey := mt.rootKey
-	var siblings []*Hash
+	siblings := []*Hash{}
 	for i := 0; i < mt.maxLevels; i++ {
 		n, err := mt.GetNode(nextKey)
 		if err != nil {
@@ -607,7 +607,7 @@ func (mt *MerkleTree) Delete(k *big.Int) error {
 	path := getPath(mt.maxLevels, kHash[:])
 
 	nextKey := mt.rootKey
-	var siblings []*Hash
+	siblings := []*Hash{}
 	for i := 0; i < mt.maxLevels; i++ {
 		n, err := mt.GetNode(nextKey)
 		if err != nil {
@@ -842,7 +842,7 @@ func (p *Proof) Bytes() []byte {
 // SiblingsFromProof returns all the siblings of the proof.
 func SiblingsFromProof(proof *Proof) []*Hash {
 	sibIdx := 0
-	var siblings []*Hash
+	siblings := []*Hash{}
 	for lvl := 0; lvl < int(proof.depth); lvl++ {
 		if TestBitBigEndian(proof.notempties[:], uint(lvl)) {
 			siblings = append(siblings, proof.Siblings[sibIdx])

merkletree_test.go

@@ -712,6 +712,15 @@ func TestSmtVerifier(t *testing.T) {
 
 	err = mt.Add(big.NewInt(1), big.NewInt(11))
 	assert.Nil(t, err)
+
+	cvp, err := mt.GenerateSCVerifierProof(big.NewInt(1), nil)
+	assert.Nil(t, err)
+	jCvp, err := json.Marshal(cvp)
+	assert.Nil(t, err)
+	// expect siblings to be '[]', instead of 'null'
+	expected := `{"root":"14137057030252181222327992235694793580963111268072013054745223667806564674729","siblings":[],"oldKey":"0","oldValue":"0","isOld0":false,"key":"1","value":"11","fnc":0}` //nolint:lll
+
+	assert.Equal(t, expected, string(jCvp))
 	err = mt.Add(big.NewInt(2), big.NewInt(22))
 	assert.Nil(t, err)
 	err = mt.Add(big.NewInt(3), big.NewInt(33))
@@ -719,14 +728,14 @@ func TestSmtVerifier(t *testing.T) {
 	err = mt.Add(big.NewInt(4), big.NewInt(44))
 	assert.Nil(t, err)
 
-	cvp, err := mt.GenerateCircomVerifierProof(big.NewInt(2), nil)
+	cvp, err = mt.GenerateCircomVerifierProof(big.NewInt(2), nil)
 	assert.Nil(t, err)
 
-	jCvp, err := json.Marshal(cvp)
+	jCvp, err = json.Marshal(cvp)
 	assert.Nil(t, err)
 	// Test vectors generated using https://github.com/iden3/circomlib smt.js
 	// Expect siblings with the extra 0 that the circom circuits need
-	expected := `{"root":"10171140035965439966839815283432442651152991056297946102647688349369299124493","siblings":["12422661758472400223401299094238820777063458096110016599986781158438915645129","4330149052063565277182642012557086942088176847773467265587998154672740895682","0","0","0"],"oldKey":"0","oldValue":"0","isOld0":false,"key":"2","value":"22","fnc":0}` //nolint:lll
+	expected = `{"root":"10171140035965439966839815283432442651152991056297946102647688349369299124493","siblings":["12422661758472400223401299094238820777063458096110016599986781158438915645129","4330149052063565277182642012557086942088176847773467265587998154672740895682","0","0","0"],"oldKey":"0","oldValue":"0","isOld0":false,"key":"2","value":"22","fnc":0}` //nolint:lll
 	assert.Equal(t, expected, string(jCvp))
 
 	cvp, err = mt.GenerateSCVerifierProof(big.NewInt(2), nil)