Tutorial by Topics: null

var result = possibleNullObject ?? defaultValue; ParameterDetailspossibleNullObjectThe value to test for null value. If non null, this value is returned. Must be a nullable type.defaultValueThe value returned if possibleNullObject is null. Must be the same type as possibleNullObject. The n...

X?.Y; //null if X is null else X.Y X?.Y?.Z; //null if X is null or Y is null else X.Y.Z X?[index]; //null if X is null else X[index] X?.ValueMethod(); //null if X is null else the result of X.ValueMethod(); X?.VoidMethod(); //do nothing if X is null else call X.VoidMethod(); Note that w...

Nullable<int> i = 10; int? j = 11; int? k = null; DateTime? DateOfBirth = DateTime.Now; decimal? Amount = 1.0m; bool? IsAvailable = true; char? Letter = 'a'; (type)? variableName Nullable types can represent all the values of an underlying type as well as null. The syntax T? i...

An error 1009 is a general error that arises when you are trying to receive a value out of a variable or property that has a value of null. The examples provided expose various cases where this error arises, together with some recommendations on how to mitigate the error. The dreaded and often ask...

NULL in SQL, as well as programming in general, means literally "nothing". In SQL, it is easier to understand as "the absence of any value". It is important to distinguish it from seemingly empty values, such as the empty string '' or the number 0, neither of which are actually ...

NullReferenceException is thrown whenever a variable is empty and one of its method/properties are referenced. To avoid this, be sure all variables are initialized correctly (new operator), and all methods returns a non-null value.

In SQL Server, NULL represents data that is missing, or unknown. This means that NULL is not really a value; it's better described as a placeholder for a value. This is also the reason why you can't compare NULL with any value, and not even with another NULL. SQL Server provides other methods...

The value null is the default value for an uninitialized value of a field whose type is a reference type. NullPointerException (or NPE) is the exception that is thrown when you attempt to perform an inappropriate operation on the null object reference. Such operations include: calling an inst...

Null Object is an object with no referenced value or with defined neutral behaviour. Its purpose is to remove the need of null pointer/reference check.

A column is NULL when it has no value, regardless of the data type of that column. A column should never be compared to NULL using this syntax a = NULL as the result would be UNKNOWN. Instead use a IS NULL or a IS NOT NULL conditions. NULL is not equal to NULL. To compare two expressions where null...

The null coalescing operator (??) has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with isset(). It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.