Null check missed guard?

[dibyendumajumdar]

This test program failed in chapter 21

struct Point { int x; };

Point?[] !points = new Point?[2];
points[arg] = new Point { x = 42; };
Point? p = points[1];

if (p != null)
    return p.x;

return -1;

Error reported

Exception in thread "main" com.seaofnodes.simple.Parser$ParseException: Might be null accessing 'x'
	at com.seaofnodes.simple.Parser.error(Parser.java:1743)
	at com.seaofnodes.simple.node.MemOpNode.err(MemOpNode.java:108)
	at com.seaofnodes.simple.node.Node._walk(Node.java:708)
	at com.seaofnodes.simple.node.Node._walk(Node.java:711)
	at com.seaofnodes.simple.node.Node._walk(Node.java:711)
	at com.seaofnodes.simple.node.Node._walk(Node.java:710)
	at com.seaofnodes.simple.node.Node._walk(Node.java:710)
	at com.seaofnodes.simple.node.Node._walk(Node.java:710)