Is there another way to set Nullable=True on a field?

We can add this attribute to a field, in order to set the Nullable=true in the swagger - but this assumes I have access to the source
[OpenApiProperty(Nullable = true, Default = 10, Description = "The number value")]

What if I dont have access to the source (e.g. I am referencing a 3rd party c# class)? Is there another way to set Nullable=true on the fields?

Start by reviewing how the extension generates OpenAPI schemas and how nullable metadata is currently supplied through OpenApiProperty on model fields. The work is done when a third-party C# type can have its fields marked nullable without modifying its source, and the generated Swagger reflects Nullable=true.

Written by the indexing model from the issue text.