feat:(ast) nill Node can marshal to null

ast/decode.go

@@ -29,8 +29,10 @@ import (
 // Hack: this is used for both checking space and cause firendly compile errors in 32-bit arch.
 const _Sonic_Not_Support_32Bit_Arch__Checking_32Bit_Arch_Here = (1 << ' ') | (1 << '\t') | (1 << '\r') | (1 << '\n')
 
+var bytesNull   = []byte("null")
+
 const (
-    bytesNull   = "null"
+    strNull   = "null"
     bytesTrue   = "true"
     bytesFalse  = "false"
     bytesObject = "{}"
@@ -64,7 +66,7 @@ func decodeNull(src string, pos int) (ret int) {
     if ret > len(src) {
         return -int(types.ERR_EOF)
     }
-    if src[pos:ret] == bytesNull {
+    if src[pos:ret] == strNull {
         return ret
     } else {
         return -int(types.ERR_INVALID_CHAR)

ast/encode.go

@@ -91,6 +91,10 @@ func quoteString(e *[]byte, s string) {
 var bytesPool   = sync.Pool{}
 
 func (self *Node) MarshalJSON() ([]byte, error) {
+	if self == nil {
+		return bytesNull, nil
+	}
+
     buf := newBuffer()
     err := self.encode(buf)
     if err != nil {
@@ -159,7 +163,7 @@ func (self *Node) encodeRaw(buf *[]byte) error {
 }
 
 func (self *Node) encodeNull(buf *[]byte) error {
-    *buf = append(*buf, bytesNull...)
+    *buf = append(*buf, strNull...)
     return nil
 }
 

ast/encode_test.go

@@ -120,7 +120,23 @@ func TestEncodeValue(t *testing.T) {
     }
 }
 
+func BenchmarkNil(b *testing.B) {
+	for i:=0; i<b.N; i++ {
+		null := (*Node)(nil)
+		_, _ = null.MarshalJSON()
+	}
+}
+
 func TestEncodeNode(t *testing.T) {
+	null := (*Node)(nil)
+	js, err := null.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(js) != "null" {
+		t.Fatal(string(js))
+	}
+
     data := `{"a":[{},[],-0.1,true,false,null,""],"b":0,"c":true,"d":false,"e":null,"g":""}`
     root, e := NewSearcher(data).GetByPath()
     if e != nil {