[E018] Error: case `Foo::Bar` of backed enum `Foo` must have a value
   ,-[code.php:5:13]
   |
 3 | enum Foo: string
   *      ^^^  
   *            
   * 
 5 |     case Bar;
   *          ^^^|  
   *             `-- try adding a value
   *                
   *                 
---'