Rule Definition
Methods that are not expected to throw exceptions can be categorized as follows: -Event Accessor Methods -Equals Methods -GetHashCode Methods -ToString Methods -Static Constructors -Dispose Methods -Equality Operators -Implicit Cast Operators Limitations: *The following exceptions can be thrown from a property get method: System.InvalidOperationException and all derivatives (including System.ObjectDisposedException) System.NotSupportedException and all derivatives System.ArgumentException (only from indexed get) KeyNotFoundException (only from indexed get) *The following exceptions can be thrown from an event accessor: System.InvalidOperationException and all derivatives (including System.ObjectDisposedException) System.NotSupportedException and all derivatives ArgumentException and derivatives *The versions of GetHashCode that take an argument can throw an ArgumentException. However, Object.GetHashCode should never throw an exception.

Remediation
Change the logic so that it no longer must throw an exception.

Violation Code Sample

public class Person : IEquatable<Person>
{
   public string lName;

  public override bool Equals(Object obj)
   {
      Person pers = obj as Person;
      if (pers == null)
         throw new ArgumentException("...");  //VIOLATION
      else
         return (this.lName== pers.lName);
   }
}

Fixed Code Sample

public class Person : IEquatable<Person>
{
   public string lName;

  public override bool Equals(Object obj)
   {
      Person pers = obj as Person;
      if (pers == null)
         return false;  // Compliant
      else
         return (this.lName== pers.lName);
   }
}

https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1065