diff --git a/roller.go b/roller.go
index 11e4a58..45431e2 100644
--- a/roller.go
+++ b/roller.go
@@ -183,6 +183,10 @@ func (r *roller) traverseMap(iface interface{}) {
 	switch t := iface.(type) {
 	case map[string]interface{}:
 		for k, v := range t {
+			// drop null values in json to prevent panic caused by reflect.TypeOf(nil)
+			if v == nil {
+				continue
+			}
 			switch reflect.TypeOf(v).Kind() {
 			case reflect.Struct:
 				r.typeName = k // set the map key as name
diff --git a/roller_test.go b/roller_test.go
index 30e2032..e6a46b7 100644
--- a/roller_test.go
+++ b/roller_test.go
@@ -83,6 +83,7 @@ func init() {
 	m["person"] = "John Doe"
 	m["iface"] = map[string]string{"another_person": "does it change root!"}
 	m["array"] = [5]int{1, 4, 5, 6, 7}
+	m["null"] = nil
 }
 
 func TestRoller_push(t *testing.T) {