import StyletronCore from "styletron-core";

declare class StyletronClient extends StyletronCore {
  constructor(els?: HTMLCollection | HTMLElement[]);
}

export default StyletronClient;

import StyletronCore from "styletron-core";

declare class StyletronClient extends StyletronCore {
  constructor(els: HTMLCollection | HTMLElement[]);
}

export default StyletronClient;

--- 
+++ 
@@ -1,7 +1,7 @@
 import StyletronCore from "styletron-core";
 
 declare class StyletronClient extends StyletronCore {
-  constructor(els: HTMLCollection | HTMLElement[]);
+  constructor(els?: HTMLCollection | HTMLElement[]);
 }
 
 export default StyletronClient;
Make argument for `StyletronClient` constructor optional
