FULL PRODUCT VERSION :
java version "1.8.0_31"
Java(TM) SE Runtime Environment (build 1.8.0_31-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.31-b07, mixed mode)

A DESCRIPTION OF THE PROBLEM :
currently DateFormat does not throw a NullPointerException when the parameter to setCalendar or setNumberFormat is null. This causes subsequent calls to the format method to fail

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Consider the following class:

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Bug {

	public static void main(String[] args) throws ParseException {
		DateFormat fmt = new SimpleDateFormat("yyyy-MM-dd");
		fmt.setCalendar(null);
		fmt.setNumberFormat(null);
		fmt.format(new Date());
	}

}


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect DateFormat to prevent callers from moving it into an illegal state. Both
fmt.setCalendar(null);
and
fmt.setNumberFormat(null);
must throw a NullPointerException in the code above
ACTUAL -
A NullPointerException is thrown at the line
fmt.format(new Date());
because its required internal variables were set to null

REPRODUCIBILITY :
This bug can be reproduced always.