NullPointerException with autoboxing in ternary expression

Question

Run the following Java code:

boolean b = false;
Double d1 = 0d;
Double d2 = null;
Double d = b ? d1.doubleValue() : d2;

Why is there a Null

Answer 1

Because the two expressions around : must return the same type. This means Java tries to convert the expression d2 to double. This means the bytecode calls doubleValue() on d2 -> NPE.