FULL PRODUCT VERSION :
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Client VM (build 16.3-b01, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Windows 7 32-bit

A DESCRIPTION OF THE PROBLEM :
unexpected NullPointerException after running

public static void main(String[] args) {
    Double a = null;
    Double b = null;
    Double c = null == a ? b : 0d;
}

Double c = null == a ? null : 0d;
will work

decompiled code
first piece
    public static void main(String args[])
    {
        Double a = null;
        Double b = null;
        Double c = Double.valueOf(a != null ? 0.0D : b.doubleValue());
    }
crystal clear, why it throws a NPE

second piece... Double c = null == a ? null : 0d; version
    public static void main(String args[])
    {
        Double a = null;
        Double b = null;
        Double c = a != null ? Double.valueOf(0.0D) : null;
    }

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
run the main method in the Description


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
c equals null
ACTUAL -
NullPointerException on line
Double c = null == a ? b : 0d;

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.NullPointerException

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public static void main(String[] args) {
    Double a = null;
    Double b = null;
    Double c = null == a ? b : 0d;
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
instead of
public static void main(String[] args) {
Double a = null;
Double b = null;
Double c = null == a ? b : 0d;
}
use
                  Double c = null == a ? null : 0d;

not much of a workaround, for often a variable is required (variable b) instead of a particular value (null)