Reject if !this.hass

src/components/thumbnail.ts

@@ -55,12 +55,16 @@ export class FrigateCardThumbnailFeatureEvent extends LitElement {
       return this.thumbnail;
     }
     return new Promise((resolve, reject) => {
-      //eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      this.hass!.fetchWithAuth(thumbnail)
-      // Since we are fetching with an authorization header, we cannot just put the
-      // URL directly into the document; we need to embed the image. We could do this
-      // using blob URLs, but then we would need to keep track of them in order to
-      // release them properly. Instead, we embed the thumbnail using base64.
+      if (!this.hass) {
+        reject();
+        return;
+      }
+      this.hass
+        .fetchWithAuth(thumbnail)
+        // Since we are fetching with an authorization header, we cannot just put the
+        // URL directly into the document; we need to embed the image. We could do this
+        // using blob URLs, but then we would need to keep track of them in order to
+        // release them properly. Instead, we embed the thumbnail using base64.
         .then((response) => response.blob())
         .then((blob) => {
           const reader = new FileReader();