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How do you check if a list is null or not?
You should do if(test!= null) instead (Checking for null first). The method isEmpty() returns true, if an ArrayList object contains no elements; false otherwise (for that the List must first be instantiated that is in your case is null ).
Can a list have NULL values?
List allows any number of null values while a set contains at most one null element. A Map typically allows null as a key and value, but some implementations prohibit null keys and values.
Can Set have null values?
A Set is a collection that cannot contain duplicate elements. It models the mathematical set abstraction. It does not allow duplicate elements and allow one null value at most.
How to check if a list is null?
It can be used like so: if (myList == null) // Checks if list is null // Wasn’t initialized else if (myList.Count == 0) // Checks if the list is empty myList.Add (“new item”); else // List is valid and has something in it // You could access the element in the list if you wanted myList [0] gets the first item in the list.
How to avoid null reference when adding object to list?
You have it defined as a List type but you never initialize it to an instance of that type. Try initializing it in a constructor: OrderiTems is null. Try implementing set/get or storing an empty list into OrderiTems in the constructor. You need to instanciate the list before starting using it.
Where do I find the null reference exception?
A good place to do that is in the class constructor. Assuming you use the default constructor : Is DbNull is not the same as Is NULL! You need to check for ‘IS NULL’, instead. That is why you are getting Null Reference Exceptions.
Why is DbNull not the same as is null?
Is DbNull is not the same as Is NULL! You need to check for ‘IS NULL’, instead. That is why you are getting Null Reference Exceptions. Not the answer you’re looking for?