json2: decode fn returns ?T; add new tests (#6933)

vlib/x/json2/builder.v

@@ -9,56 +9,69 @@ pub fn (mut obj map[string]Any) insert_str(key string, val string) {
 	fi = val
 	obj[key] = fi
 }
+
 // Inserts an int into the map.
 pub fn (mut obj map[string]Any) insert_int(key string, val int) {
 	obj[key] = Any(val)
 }
+
 // Inserts a float into the map.
 pub fn (mut obj map[string]Any) insert_f(key string, val f64) {
 	obj[key] = Any(val)
 }
+
 // Inserts a null into the map.
 pub fn (mut obj map[string]Any) insert_null(key string) {
 	obj[key] = Any(Null{})
 }
+
 // Inserts a bool into the map.
 pub fn (mut obj map[string]Any) insert_bool(key string, val bool) {
 	obj[key] = Any(val)
 }
+
 // Inserts a map into the map.
 pub fn (mut obj map[string]Any) insert_map(key string, val map[string]Any) {
 	obj[key] = Any(val)
 }
+
 // Inserts an array into the map.
 pub fn (mut obj map[string]Any) insert_arr(key string, val []Any) {
 	obj[key] = Any(val)
 }
+
 // Inserts a string into the array.
 pub fn (mut arr []Any) insert_str(val string) {
 	mut fi := Any{}
 	fi = val
 	arr << fi
 }
+
 // Inserts an int into the array.
 pub fn (mut arr []Any) insert_int(val int) {
 	arr << Any(val)
 }
+
 // Inserts a float into the array.
 pub fn (mut arr []Any) insert_f(val f64) {
 	arr << Any(val)
 }
+
 // Inserts a null into the array.
 pub fn (mut arr []Any) insert_null() {
 	arr << Any(Null{})
 }
+
 // Inserts a bool into the array.
 pub fn (mut arr []Any) insert_bool(val bool) {
 	arr << Any(val)
 }
+
 // Inserts a map into the array.
 pub fn (mut arr []Any) insert_map(val map[string]Any) {
 	arr << Any(val)
 }
+
 // Inserts an array into the array.
 pub fn (mut arr []Any) insert_arr(val []Any) {
 	arr << Any(val)