src/main/java/io/reactivex/Notification.java
@SuppressWarnings("unchecked")
    @Nullable
    public T getValue() {
        Object o = value;
        if (o != null && !NotificationLite.isError(o)) {
            return (T)value;
        }
        return null;
    }
@SuppressWarnings("unchecked")
    @Nullable
    public T getValue() {
        Object o = value;
        if (o != null && !NotificationLite.isError(o)) {
            return (T)value;
        }
        return null;
    }
Returns the contained value if this notification is an onNext
signal, null otherwise.
@return the value contained or null
@see #isOnNext()