Build fails when no macros are used

[Nicolò Balzarotti]

when no macros are used in a mugur definition, the keymap.c file contains something like:

      bool process_record_user(uint16_t keycode, keyrecord_t *record) {
          if (record->event.pressed) {
              switch (keycode) {
                 case EPRM:
                 eeconfig_init();
                 return false;
              nil
         nil
      	      }
          }

and

      enum custom_keycodes {
          EPRM = SAFE_RANGE,
          nil, 
       nil
      };