Merge pull request #15513 from overleaf/jpa-consistent-return-type

[web] ExpressLocals: avoid returning undefined from getCssThemeModifier

GitOrigin-RevId: f5256719c2b4f06e2957f6bc971d3c895bdff5d2

services/web/app/src/infrastructure/ExpressLocals.js

@@ -212,6 +212,7 @@ module.exports = function (webRouter, privateApiRouter, publicApiRouter) {
           return userSettings.overallTheme
         }
       }
+      return ''
     }
 
     res.locals.buildStylesheetPath = function (cssFileName) {