Why does the Java compiler sometimes allow the unboxing of null?

For example:

int anInt = null;

fails at compile time but

public static void main(String[] args) {
  for (int i = 0; i < 10; i++) {
    System.out.println("" + getSomeVal());
  }
}
public static int getSomeVal() {
   return new Random().nextBoolean() ? 1 : null;
}

fails (usually) at run time. Trying to return just null will also result in a compile error, so I assume there is something about having multiple paths that causes the compiler to infer that null is potentially an autoboxed int? Why can javac not fail to compile both cases with the same error?