only merge the first-level fields of json, and assign values directly…

… to deeper fields

merge.go

@@ -20,8 +20,7 @@ func merge(cur, patch *lazyNode, mergeMerge bool) *lazyNode {
 	if err != nil {
 		return patch
 	}
-
-	mergeDocs(curDoc, patchDoc, mergeMerge)
+	mergeDocs2(curDoc, patchDoc, mergeMerge)
 
 	return cur
 }
@@ -50,6 +49,24 @@ func mergeDocs(doc, patch *partialDoc, mergeMerge bool) {
 	}
 }
 
+func mergeDocs2(doc, patch *partialDoc, mergeMerge bool) {
+	for k, v := range *patch {
+		if v == nil {
+			if mergeMerge {
+				(*doc)[k] = nil
+			} else {
+				delete(*doc, k)
+			}
+		} else {
+			if !mergeMerge {
+				pruneNulls(v)
+			}
+
+			(*doc)[k] = v
+		}
+	}
+}
+
 func pruneNulls(n *lazyNode) {
 	sub, err := n.intoDoc()
 

print.go

@@ -0,0 +1,17 @@
+package jsonpatch
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+)
+
+func PrintJson(data []byte) {
+	var out bytes.Buffer
+	err := json.Indent(&out, data, "", "    ")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(out.String())
+}