docs(contributing): improve code format in checking for undefined o…

…r `null`

Co-authored-by: Jan Romann <[email protected]>

CONTRIBUTING.md

@@ -94,17 +94,17 @@ How then should the contributor deal with nullable variables? For example:
 ```ts
 function(arg1: string | null | undefined) {
     // ERROR: not allowed by strict-boolean-expressions
-    if(!arg) { throw new Error("arg should be defined!))}
+    if (!arg) { throw new Error("arg should be defined!); }
 }
 ```
 
-Instead of checking for both null and `undefiend` values (`if(arg !== undefined && arg !== null)`) the preferred solution is to use `!=` or `==` operator. Interestingly in JavaScript
-with ==, null and undefined are only equal to each other. Example:
+Instead of checking for both null and `undefined` values (`if (arg !== undefined && arg !== null)`) the preferred solution is to use `!=` or `==` operator. Interestingly in JavaScript
+with `==`, `null` and `undefined` are only equal to each other. Example:
 
 ```ts
 function(arg1: string | null | undefined) {
     // OK
-    if(arg == null) { throw new Error("arg should be defined!))}
+    if (arg == null) { throw new Error("arg should be defined!); }
 }
 ```