make json work with new optionals

compiler/tests/struct_test.v

@@ -0,0 +1,44 @@
+struct A{
+mut: 
+	val int 
+	nums []int 
+} 
+
+struct B{
+mut: 
+	a A 
+} 
+struct C {
+mut: 
+	b B 
+	nums []int 
+	as []A 
+	num int 
+} 
+ 
+fn test_struct_levels() { 
+	mut c := C{} 
+	assert c.nums.len == 0 
+	c.nums << 3 
+	assert c.nums.len == 1 
+	assert c.nums[0] == 3 
+	c.nums[0] = 4 
+	assert c.nums[0] == 4 
+	c.b.a.val = 34 
+	assert c.b.a.val == 34 
+	c.b.a.nums = [0;0] 
+	c.b.a.nums << 0 
+	c.b.a.nums << 2 
+	assert c.b.a.nums.len == 2 
+	assert c.b.a.nums[0] == 0 
+	assert c.b.a.nums[1] == 2 
+	c.b.a.nums [0] = 7 
+	assert c.b.a.nums[0] == 7 
+	c.as << A{val:8} 
+	assert c.as.len == 1 
+	assert c.as[0].val == 8 
+	c.num = 20 
+	assert c.num == 20 
+	c.as[0].val  = 10 
+	assert c.as[0].val == 10 
+}