Problem with implicit data type conversion in Javascript

app.yaml

# Google App Engine configation
env_variables:
  FEATURE_CORS_ENABLED: false

middleware.js

export const configureMiddlewares = (app) => {
  if (FEATURE_CORS_ENABLED) {
   // Do some stuff that enables CORS
  }       
  
   app.use((err, res, next) => {
        if (err.message === "CORS") {
            res.status(401).send(
                "The CORS policy for this site does not allow access from the specified Origin."
            );
        }
        next();
    });
}

The existence of a string is true:

Google App Engine configuration: Transforming YAML to JSON:

Google App Engine configuration after deployment: