bugfix: get key from null

Author: rhtang

jsonpath.go

@@ -12,6 +12,8 @@ import (
 	"errors"
 )
 
+var ErrGetFromNullObj = errors.New("get attribute from null object")
+
 func JsonPathLookup(obj interface{}, jpath string) (interface{}, error) {
 	steps, err := tokenize(jpath)
 	//fmt.Println("f: steps: ", steps, err)
@@ -276,6 +278,9 @@ func filter_get_from_explicit_path(obj interface{}, path string) (interface{}, e
 }
 
 func get_key(obj interface{}, key string) (interface{}, error) {
+	if reflect.TypeOf(obj) == nil {
+		return nil, ErrGetFromNullObj
+	}
 	switch reflect.TypeOf(obj).Kind() {
 	case reflect.Map:
 		for _, kv := range reflect.ValueOf(obj).MapKeys() {

jsonpath_test.go

@@ -943,3 +943,17 @@ func Test_jsonpath_string_equal(t *testing.T) {
 		t.Fatalf("not the same: %v", res)
 	}
 }
+
+func Test_jsonpath_null_in_the_middle(t *testing.T) {
+	data := `{
+  "head_commit": null,
+}
+`
+
+	var j interface{}
+
+	json.Unmarshal([]byte(data), &j)
+
+	res, err := JsonPathLookup(j, "$.head_commit.author.username")
+	t.Log(res, err)
+}