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Code Analyzer for C#

There is a newer version: 10.2.0.105762

Why is this an issue?
Calling GetType() on a nullable value type object returns
the underlying value type. Therefore, comparing the returned Type
object to typeof(Nullable<SomeType>) will either throw an NullReferenceException or the result will always be
true or false and can be known at compile time.
How to fix it
Code examples
Noncompliant code example
void DoChecks<T>(Nullable<T> value) where T : struct
{
    bool areEqual = value.GetType() == typeof(Nullable<int>); // Noncompliant: always false
    bool areNotEqual = value.GetType() != typeof(Nullable<int>); // Noncompliant: always true

    Nullable<int> nullable = null;
    bool nullComparison = nullable.GetType() != typeof(Nullable<int>); // Noncompliant: throws NullReferenceException
}

Compliant solution
void DoChecks<T>(Nullable<T> value) where T : struct
{
    bool areEqual = value.GetType() == typeof(int); // Compliant: can be true or false
    bool areNotEqual = value.GetType() != typeof(int); // Compliant: can be true or false

    Nullable<int> nullable = null;
    bool nullComparison = nullable is not null && nullable.GetType() == typeof(int); // Compliant: does not throw NullReferenceException
}

Resources
Documentation

   Microsoft Learn - Object.GetType Method 
   Microsoft Learn - Nullable
  value types (C# reference) 
   Microsoft Learn - Type Class 
   Microsoft Learn - NullReferenceException Class