Merge pull request #77 from Dot-Liu/master

修复编排取值空指针的问题

node/gateway/application/interpreter/reader.go

@@ -49,6 +49,12 @@ func (r *_BodyReader) Read(variables *Variables) string {
 func find(node *reflect.Value, path []string) string {
 
 	if len(path) == 0 {
+		if !node.IsValid(){
+			return ""
+		}
+		if node.IsNil(){
+			return ""
+		}
 		return fmt.Sprint(node.Interface())
 	}