Null object or null reference in list

[Bilal Waqar]

Hi Group,

I am working on project to use cofoja to write contracts and I am stuck at place where I have to check if list is null or have null reference and no in world I can write pre condition for that.

This is my method: 

@Requires("n != null") 

public void push(Object o) {

numbers.add(o);

}

This is my test to check if I vioalte precondition

@Test 

public void PushFailTest () {

assertThrows(PreconditionError.class, () -> {

list.push(null);

});

}