fix(drizzle-zod): apply ZodOptional for insert schema refinements on nullable/default columns

[swalha1999]

Problem

When using function refinements in createInsertSchema, the type inference was not correctly applying ZodOptional for:

• Nullable columns (should be optional since they can be omitted)
• NotNull columns with defaults (should be optional since defaults will be used)

This caused a type mismatch where the inferred type was string | null but the runtime schema correctly produced string | null | undefined.

Example

const blogPost = pgTable("blog_post", {
  id: uuid("id").primaryKey().defaultRandom(),
  title: text("title").notNull(),
  metaTitle: text("meta_title"), // nullable, no default
});

const insertSchema = createInsertSchema(blogPost, {
  metaTitle: (schema) => schema.max(60, "Too long"),
});

// Before fix: metaTitle inferred as `string | null` (missing undefined)
// After fix: metaTitle inferred as `string | null | undefined`

Solution

The fix aligns HandleRefinement type with HandleInsertColumn logic:

• For nullable columns: z.ZodOptional<z.ZodNullable<TSchema>>
• For notNull with default: z.ZodOptional<TSchema>
• For notNull without default: TSchema (required)

Changes

• Updated HandleRefinement type in drizzle-zod/src/schema.types.internal.ts

Testing

All 70 existing drizzle-zod tests pass.