/** Merges the `defaults` object of type `T` into the `formData` of type `T`
 *
 * When merging defaults and form data, we want to merge in this specific way:
 * - objects are deeply merged
 * - arrays are merged in such a way that:
 *   - when the array is set in form data, only array entries set in form data
 *     are deeply merged; additional entries from the defaults are ignored unless `mergeExtraArrayDefaults` is true, in
 *     which case the extras are appended onto the end of the form data
 *   - when the array is not set in form data, the default is copied over
 * - scalars are overwritten/set by form data
 *
 * @param [defaults] - The defaults to merge
 * @param [formData] - The form data into which the defaults will be merged
 * @param [mergeExtraArrayDefaults=false] - If true, any additional default array entries are appended onto the formData
 * @returns - The resulting merged form data with defaults
 */
export default function mergeDefaultsWithFormData<T = any>(defaults?: T, formData?: T, mergeExtraArrayDefaults?: boolean): T | undefined;