I have the following Zod schema:

const schema = z.object({
    nested1: z.object({
        nested2: z.object({
            nested3: z.string(),
            dummy1: z.string(),
            dummy2: z.string(),
        }),
    }),
});

And I try to build a new schema which would look like the original but with some .catch() statements:

const secondSchema = z.object({
    nested1: z.object({
        nested2: z.object({
            nested3: z.string().catch(null),
            dummy1: z.string(),
            dummy2: z.string(),
        }),
    }),
});

I would like to extend the original schema with the least duplicate code.
Right now the fields dummy1 and dummy2 are duplicated.

I try to get something like:

const secondSchema = schema.extend({
    nested1: z.object({
        nested2: z.object({
            nested3: z.string().catch(null),
        }),
    }),
});

But this code would remove dummy1 and dummy2 off the schema because I overwrite nested2

How can I do it with least duplicate code?