null C# with Example
A variable of a reference type can hold either a valid reference to an instance or a null reference. The null reference
is the default value of reference type variables, as well as nullable value types.
null is the keyword that represents a null reference.
As an expression, it can be used to assign the null reference to variables of the aforementioned types:
object a = null;
string b = null;
int? c = null;
List d = null;
Non-nullable value types cannot be assigned a null reference. All the following assignments are invalid:
int a = null;
float b = null;
decimal c = null;
The null reference should not be confused with valid instances of various types such as:
an empty list (new List())
an empty string ("")
the number zero ( , 0f, 0m)
the null character ( '\0' )
Sometimes, it is meaningful to check if something is either null or an empty/default object. The
System.String.IsNullOrEmpty(String) method may be used to check this, or you may implement your own equivalent
private void GreetUser(string userName)
//The method that called us either sent in an empty string, or they sent us a null reference.
Either way, we need to report the problem.
throw new InvalidOperationException("userName may not be null or empty.");
//userName is acceptable.
Console.WriteLine("Hello, " + userName + "!");