Type safety not catching null/undefined arrays in generated types

## Type safety not catching null/undefined arrays in generated types

### Description
When using react-relay's generated types, TypeScript is not catching potential null/undefined arrays in the GraphQL response. This leads to runtime errors that should be caught at compile time.

### Reproduction
Given this GraphQL fragment:

`graphql
fragment SiteLoadGraphFragment on ChargingSite {
chargers {
connectors {
filteredChargingSchedule: chargingSchedule(
where: { startTime: $dateFilter, endTime: $dateFilter }
) {
id
startTime
endTime
timeTarget
energyTarget
loads {
start
stop
load
}
}
}
}
}`

And this component code:

```
function SiteLoadGraph({ data, timeWindow }: SiteLoadGraphProps) {
const siteData = useFragment(SiteLoadGraphData, data);
const getLoadOverTime = (chargers: Charger, timeWindow: StartEndTimes) => {
mutableChargers.forEach((charger) => {
charger.connectors.forEach((connector) => {
// This line throws at runtime but TypeScript doesn't catch it
connector.filteredChargingSchedule.forEach((schedule) => {
// ...
});
});
});
};
// ...
}
```

### Expected Behavior
TypeScript should warn about potential null/undefined values when trying to call `.forEach()` on `filteredChargingSchedule` without first checking if it exists and is an array.

### Actual Behavior
No TypeScript errors are shown, but at runtime we get:

`Uncaught TypeError: Cannot read properties of undefined (reading 'forEach')`

### Questions
1. Why aren't the generated types preserving nullability information from the GraphQL schema?
2. Should we be handling this differently in our code?
3. Is this a configuration issue with the GraphQL codegen?

### Environment
- react-relay version: 18.1.0
- TypeScript version: 5.3.3
- relay-compiler version:18.1.0

### Additional Context
This is particularly important for type safety as these kinds of runtime errors should be caught during development. The current behavior defeats the purpose of using TypeScript with GraphQL's type generation.

Start with the react-relay 18.1.0 reproduction and inspect the generated types produced by relay-compiler for the shown SiteLoadGraphFragment. Compare the generated nullability for chargers, connectors, and filteredChargingSchedule with the GraphQL schema and compiler configuration; done means the reproduction produces a TypeScript error for an unchecked .forEach() call.

Written by the indexing model from the issue text.