fix: nullpointer

[MeikelLP]

I'm trying to add endpoint definitions manually via IApiDescriptionProvider but as soon as I add ApiDescription.SupportedResponseTypes the swagger generator crashes due to a simple nullpointer.

The compiler and IDE even warns about this issue but it is ignored and this exception is expected to happen when MethodInfo ist null

Workaround

// add some MethodInfo to EndpointMetadata
ActionDescriptor = new ActionDescriptor
{
    EndpointMetadata = [MethodBase.GetCurrentMethod()!]
}