Why is this an issue?
The point of having custom exception types is to convey more information than is available in standard types. But custom exception types must be
public for that to work.
If a method throws a non-public exception, the best you can do on the caller’s side is to
catch the closest
of the class. However, you lose all the information that the new exception type carries.
This rule will raise an issue if you directly inherit one of the following exception types in a non-public class:
How to fix it
Noncompliant code example
internal class MyException : Exception // Noncompliant
public class MyException : Exception