Solution Object reference not set to an instance of an object

The following code will throw a NullReferenceException if the variable “text” being passed in is null. You can’t call ToUpper() on a null string.

public void MyMethod(string text)
{
     //Throws exception if text == null
     if (text.ToUpper() == "Hello World")
     {
          //do something
     }
}

You can also have null reference exceptions because any type of object is null. 

SqlCommand command = null;
//Exception! Object reference not set to an instance of an object
command.ExecuteNonQuery();

Use the Null Conditional Operator to Avoid NullReferenceExceptions

text?.ToUpper(); //from previous example, would return null

int? length = customerList?.Length; // null if customerList is null   
Customer first = customerList?[0];  // null if customerList is null  
int? count = customerList?[0]?.Orders?.Count();  // null if customerList, the first customer, or Orders is null  

Use Null Coalescing to Avoid NullReferenceExceptions

The following code throws an exception without the null coalescing. Adding “?? new List<string>()” prevents the “Object reference not set to an instance of an object” exception.

List<string> values = null;

foreach (var value in values ?? new List<string>())
{
    Console.WriteLine(value);
}