fix(isEmptyOrWhitespace): avoid exception throwing when passed value is undefined

the req.body value from "routes/api/branches" actually seems to never get parsed into a JS object, but arrives as text string, so req.body.prefix could be undefined, which of course would cause an error to be thrown, when trying to call "match" on undefined.

src/routes/api/branches.ts

@@ -216,6 +216,7 @@ function deleteBranch(req: Request) {
 
 function setPrefix(req: Request) {
     const branchId = req.params.branchId;
+    //TriliumNextTODO: req.body arrives as string, so req.body.prefix will be undefined – did the code below ever even work?
     const prefix = utils.isEmptyOrWhitespace(req.body.prefix) ? null : req.body.prefix;
 
     const branch = becca.getBranchOrThrow(branchId);

src/services/utils.ts

@@ -71,8 +71,9 @@ export function hash(text: string) {
     return crypto.createHash("sha1").update(text).digest("base64");
 }
 
-export function isEmptyOrWhitespace(str: string) {
-    return str === null || str.match(/^ *$/) !== null;
+export function isEmptyOrWhitespace(str: string | null | undefined) {
+    if (!str) return true;
+    return str.match(/^ *$/) !== null;
 }
 
 export function sanitizeSqlIdentifier(str: string) {