schema-codegen generates nullable @strawberry.input fields as required (missing Python default), causing __init__() missing required keyword-only argument for {} inputs

Describe the bug

When using strawberry schema-codegen on an SDL that contains an input with a nullable field, the generated Python @strawberry.input class annotates the field as T | None but does not assign a default value (e.g. = strawberry.UNSET or = None).

Because Strawberry input classes are dataclasses, this makes the field a required keyword-only argument in __init__, even though the GraphQL field is nullable/optional and can be omitted (e.g. input: {}).

This leads to runtime errors like:

HealthResultInput.__init__() missing 1 required keyword-only argument: 'some_number'

Minimal reproduction

SDL (schema.graphql)

type HealthResult {
  someNumber: Int
}

input HealthResultInput {
  someNumber: Int
}

type Query {
  healthy(input: HealthResultInput!): HealthResult!
}

Generate code

strawberry schema-codegen schema.graphql -o schema.py

Generated output (problem)

import strawberry

@strawberry.input
class HealthResultInput:
    some_number: int | None  # <- no default, becomes required kw-only in __init__

Query that should work (field omitted)

query MyQuery {
  healthy(input: {}) {
    someNumber
  }
}

Actual result

GraphQL returns an error because HealthResultInput() cannot be constructed from {} due to the missing Python default:

{
  "data": null,
  "errors": [
    {
      "message": "HealthResultInput.__init__() missing 1 required keyword-only argument: 'some_number'",
      "path": ["healthy"]
    }
  ]
}

Expected behavior

For nullable fields in generated @strawberry.input classes, schema-codegen should emit a Python default so the field is truly optional at runtime, for example:

• If the SDL field has no default:
  • generate = strawberry.UNSET (so omitted vs null can be distinguished), or at least = None
• If the SDL field has a default (e.g. someNumber: Int = 5):
  • generate = 5

Example expected code (no SDL default):

@strawberry.input
class HealthResultInput:
    some_number: int | None = strawberry.UNSET

Example expected code (SDL default):

@strawberry.input
class HealthResultInput:
    some_number: int | None = 5

Environment

• OS: macOS (darwin)
• Python: 3.13.x
• Strawberry: strawberry-graphql[cli,fastapi] >= 0.289.3
• Command: strawberry schema-codegen …

Additional context / related

• Input types docs (optional input fields need defaults): https://strawberry.rocks/docs/types/input-types
• Schema-codegen docs: https://strawberry.rocks/docs/codegen/schema-codegen
• Umbrella issue: https://github.com/strawberry-graphql/strawberry/issues/3097

Workarounds tried

• Manually editing generated code to add = strawberry.UNSET / = None
• Avoiding schema-codegen and writing input types code-first

Proposed fix

Update schema-codegen to:

• propagate SDL default values into Python defaults for @strawberry.input fields, and/or
• for nullable input fields with no SDL default, emit = strawberry.UNSET (or = None) so omitted fields don’t break input construction.