Possible NullPointerException on Java Unboxing

What is unboxing?

Transfer a boxed object to primary types:

Boolean->boolean, Integer->int, Double->double.

Example :

Double min = decimalMetadata.getMinValue();

…

String minString = Double.toString( min );

API: public static String toString(double d)

Why a Double object can be used as parameter which require a double value?

When unboxing happened?

unboxing is done automatically by compiler in background…

Actually the code is same as below,

Double min = decimalMetadata.getMinValue();

…

String minString = Double.toString( min.doubleValue() ); //NPE problem may happen here.

See bytecode in *.class file:

     2  aload_1 [min]

     3  invokevirtual java.lang.Double.doubleValue() : double [165]

     6  invokestatic java.lang.Double.toString(double) : java.lang.String [171]