diff --git a/json.go b/json.go
index ee6f6c1..0fdb977 100644
--- a/json.go
+++ b/json.go
@@ -181,7 +181,13 @@ func (oj *ownJSON) MergeDataForMap(ignoreError bool, dataList ...any) (map[strin
 		}
 
 		for k, v := range itemRes {
-			res[k] = v
+			if v == nil {
+				if _, exist := res[k]; !exist {
+					res[k] = v
+				}
+			} else {
+				res[k] = v
+			}
 		}
 	}
 	return res, nil