Java – toArray (t []) method in ArrayList

When I implemented it through ArrayList, I found a strange piece of code in the toArray (t []) method

public <T> T[] toArray(T[] a) {
        if (a.length < size)
            // Make a new array of a's runtime type,but my contents:
            return (T[]) Arrays.copyOf(elementData,size,a.getClass());
        System.arraycopy(elementData,a,size);
        if (a.length > size)
            a[size] = null;
        return a;
    }

This part is,

if (a.length > size)
    a[size] = null;

Why is only the element at this index in the array set to null? Once the array fills the contents of the list, the elements at the remaining indexes should be set to null, right? Or what am I missing here?

Solution

Javadoc explains why: