¿Por qué este Context NO necesita | undefined a diferencia del ejemplo anterior?

type Theme = "light" | "dark";

const ThemeContext = createContext<Theme>("light");

const useTheme = () => useContext(ThemeContext);

const ThemeProvider = ({ children }: { children: React.ReactNode }) => {
  const [theme, setTheme] = useState<Theme>("light");
  return (
    <ThemeContext.Provider value={theme}>
      {children}
    </ThemeContext.Provider>
  );
};