System.NullReferenceException

A System.NullReferenceException occurs when you try to access a member or method of a null object reference. In other words, you are trying to use an object that has not been initialized, resulting in a null value.

Here’s an example:

string s = null;

int length = s.Length; // Throws NullReferenceException

In this example, the variable s is set to null, so when we try to access its Length property, we get a NullReferenceException.

To fix this, you need to ensure that the object reference is not null before accessing its members. Here’s an updated example:

string s = null;

if (s != null)

{

int length = s.Length;

}

In this example, we check whether s is null before accessing its Length property. If it is null, we skip the code block and avoid the NullReferenceException. If it is not null, we can safely access its Length property. There are several other ways that a NullReferenceException can occur, such as accessing a property or method of an object that was expected to be initialized by a previous call but wasn’t. To avoid these types of errors, always check object references before using them and ensure that they have been properly initialized.