introduce null in writers methods

Author: shemogumbe

packages/serialization/multipart/src/multipartSerializationWriter.ts

@@ -90,7 +90,7 @@ export class MultipartSerializationWriter implements SerializationWriter {
 		// eslint-disable-next-line @typescript-eslint/no-unused-vars
 		_key?: string,
 		// eslint-disable-next-line @typescript-eslint/no-unused-vars
-		_values?: T[] | null,
+		_values?: T[],
 	): void => {
 		throw new Error(`serialization of collections is not supported with multipart`);
 	};