Enable strictNullCheck (See: https://mozilla.github.io/nunjucks/api.html#constructor)

types/nunjucks/index.d.ts

@@ -61,7 +61,7 @@ export class Environment {
         autoescape: boolean;
     };
 
-    constructor(loader?: ILoader | ILoader[], opts?: ConfigureOptions);
+    constructor(loader?: ILoader | ILoader[] | null, opts?: ConfigureOptions);
     render(name: string, context?: object): string;
     render(name: string, context?: object, callback?: (err: any, res: string) => any): void;
 

types/nunjucks/tsconfig.json

@@ -6,7 +6,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "strictFunctionTypes": true,
         "baseUrl": "../",
         "typeRoots": [
@@ -20,4 +20,4 @@
         "index.d.ts",
         "nunjucks-tests.ts"
     ]
-}
+}