When a struct is reached via *T, generateSchemaRefFor sets
schema.Nullable=true to encode nullability of that one reference site.
With ExportComponentSchemas on, that same body becomes the canonical
component definition shared by every $ref site, so the nullable flag
leaks into the component itself. Codegen tools (Orval, openapi-typescript)
then emit broken types like `interface Foo {...} | null`.

Clear the flag right before registering the schema as a component.

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Co-authored-by: Tommy Nacass <tommy.nacass@gmail.com>

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