img can be HTMLImgElement | null not undefined

Co-authored-by: Alexander Coles <a.coles@openproject.com>

Author: akabiru

app/components/primer/open_project/avatar_fallback.ts

@@ -1,16 +1,16 @@
-import {attr, controller} from '@github/catalyst'
+import { attr, controller } from '@github/catalyst'
 
 @controller
 export class AvatarFallbackElement extends HTMLElement {
   @attr uniqueId = ''
   @attr altText = ''
   @attr fallbackSrc = ''
 
-  private img?: HTMLImageElement
+  private img: HTMLImageElement | null = null
   private boundErrorHandler?: () => void
 
   connectedCallback() {
-    this.img = this.querySelector<HTMLImageElement>('img') ?? undefined
+    this.img = this.querySelector<HTMLImageElement>('img') ?? null
     if (!this.img) return
 
     this.boundErrorHandler = () => this.handleImageError(this.img!)
@@ -31,7 +31,7 @@ export class AvatarFallbackElement extends HTMLElement {
       this.img.removeEventListener('error', this.boundErrorHandler)
     }
     this.boundErrorHandler = undefined
-    this.img = undefined
+    this.img = null
   }
 
   private isImageBroken(img: HTMLImageElement): boolean {