Sometimes, merging objects with spread results in TS losing its way with inferences. It starts to complain about potential `undefined`. You COULD use type assertions......

index.ts

// Merges additional properties into an object, ensuring type consistency.
export const mergeProperties = <T, U>(
  originalObject: T,
  additionalProps: U,
): T & U => {
  return { ...originalObject, ...additionalProps };
};