add IsNull helper method

gjson.go

@@ -571,6 +571,15 @@ func (t Result) Exists() bool {
 	return t.Type != Null || len(t.Raw) != 0
 }
 
+// IsNull returns true if type is Null.
+//
+//  if gjson.Get(json, "name.nullable").IsNull() {
+//		println("value is null")
+//  }
+func (t Result) IsNull() bool {
+	return t.Type == Null
+}
+
 // Value returns one of these types:
 //
 //	bool, for JSON booleans

gjson_test.go

@@ -136,7 +136,8 @@ var basicJSON = `{"age":100, "name":{"here":"B\\\"R"},
 			}
     	]
 	},
-	"lastly":{"yay":"final"}
+	"lastly":{"yay":"final"},
+	"nullable": null
 }`
 var basicJSONB = []byte(basicJSON)
 
@@ -240,6 +241,12 @@ func TestIsArrayIsObject(t *testing.T) {
 	assert(t, !mtok.IsArray())
 }
 
+func TestIsNull(t *testing.T) {
+	value := get(basicJSON, "nullable")
+	assert(t, value.IsNull())
+	assert(t, value.Exists())
+}
+
 func TestPlus53BitInts(t *testing.T) {
 	json := `{"IdentityData":{"GameInstanceId":634866135153775564}}`
 	value := Get(json, "IdentityData.GameInstanceId")