The analyzer has detected a situation where a potentially null value is passed to expression under throw. When passing null to a throw expression, the .NET runtime will generate a NullReferenceException, although no actual dereference will have occurred in the code.
For example, in the following code:
private Exception GetException(String message)
{
if (message == null)
return null;
return new Exception(message);
}
....
throw GetException(message);a null value will be passed to the expression under throw if the 'message' parameter has the null value.
A behavior like that may be non-obvious or undesirable from the viewpoint of further handling of the exception. First, the stack of the NullReferenceException, generated at the time of executing the throw expression, will be referring to the throw expression itself rather than the cause of the exception (i.e. the return of the null value by the 'GetException' method). Second, throwing a NullReferenceException in this case does not look appropriate since no actual null dereference has occurred, and that contradiction may hinder subsequent debugging.
To make debugging easier in situations like that, either check the value returned by the 'GetException' method before any exception is thrown or, instead of returning null, have the method throw an exception that would more specifically describe the issue of passing an unexpected value to the method.
This is what the fixed version could look like:
private Exception GetException(String message)
{
if (message == null)
throw new ArgumentException();
return new Exception(message);
}