Given the following Java code:

public class Sample $\{$

public static void main$($String$[]$ args$)\{$

Sample obj $=$ null;

obj.printMessage$()$;

$\}$

public void printMessage$()\{$

System.out.println$("$Hello$,$ World!"$)$;

$\}$

$\}$

What will happen when the code is executed?

a$.$ Runtime error

b$.$ Hello, World:

c$.$ null

d$.$ Compilation error