update signature

src/stream/stream-filter-transformer.ts

@@ -4,7 +4,7 @@ import {Transform, TransformOptions} from 'stream';
  * Options interface
  */
 export interface IStreamFilterOptions extends TransformOptions {
-    filter: (chunk: any, encode: string) => [null | string, any];
+    filter: (chunk: any, encode: string) => [null | string, any]|[null];
 }
 
 /**