refactor: raise Typescript version to 4.4.4

package-lock.json

@@ -8970,9 +8970,9 @@
       }
     },
     "typescript": {
-      "version": "3.9.10",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.9.10.tgz",
-      "integrity": "sha512-w6fIxVE/H1PkLKcCPsFqKE7Kv7QUwhU8qQY2MueZXWx5cPZdwFupLgKK3vntcK98BtNHZtAF4LA/yl2a7k8R6Q==",
+      "version": "4.4.4",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.4.4.tgz",
+      "integrity": "sha512-DqGhF5IKoBl8WNf8C1gu8q0xZSInh9j1kJJMqT3a94w1JzVaBU4EXOSMrz9yDqMT0xt3selp83fuFMQ0uzv6qA==",
       "dev": true
     },
     "uglify-js": {

package.json

@@ -89,7 +89,7 @@
     "supertest": "6.2.2",
     "tslint": "6.1.3",
     "typedoc": "0.22.13",
-    "typescript": "3.9.10"
+    "typescript": "4.4.4"
   },
   "nyc": {
     "all": true,

src/notification/backend-transport.ts

@@ -35,7 +35,7 @@ export class BackendTransport {
   /**
    * One (and only one) instance of the backend transport
    */
-  private static _instance: BackendTransport;
+  private static _instance?: BackendTransport;
 
   /**
    * Stores information if transport is in state of waiting for the verification

tsconfig.json

@@ -1,7 +1,8 @@
 {
   "extends": "./node_modules/@openstapps/configuration/tsconfig.json",
   "compilerOptions": {
-    "resolveJsonModule": true
+    "resolveJsonModule": true,
+    "useUnknownInCatchVariables": false
   },
   "exclude": [
     "./config/",