kv: update comments

kv/index_iter.go

@@ -152,7 +152,7 @@ func (c *kvIndex) GenIndexKey(indexedValues []interface{}, h int64) (key []byte,
 }
 
 // Create creates a new entry in the kvIndex data.
-// If the index is unique and there already exists an entry with the same key, Create will return ErrKeyExists.
+// If the index is unique and it already existed an entry with the same key, Create will return ErrKeyExists.
 func (c *kvIndex) Create(rm RetrieverMutator, indexedValues []interface{}, h int64) error {
 	key, distinct, err := c.GenIndexKey(indexedValues, h)
 	if err != nil {

kv/iter.go

@@ -65,7 +65,7 @@ func DecodeValue(data []byte) ([]interface{}, error) {
 }
 
 // NextUntil applies FnKeyCmp to each entry of the iterator until meets some condition.
-// It will stop when fn returns true, or iterator is invalid or occur error.
+// It will stop when fn returns true, or iterator is invalid or occur errors.
 func NextUntil(it Iterator, fn FnKeyCmp) error {
 	var err error
 	for it.Valid() && !fn([]byte(it.Key())) {