docs: public void removeSlot(TimeSlot oldSlot) {
  
          if (oldSlot.nextEntry != null) {
              oldSlot.nextEntry.prevEntry = oldSlot.prevEntry;
          } else {
              // old slot was tail.
              this.lastSlot = oldSlot.prevEntry;
          }
  
          if (oldSlot.prevEntry != null) {
              oldSlot.prevEntry.nextEntry = oldSlot.nextEntry;
          } else {
              // oldSlot was head.
              this.firstSlot = oldSlot.nextEntry;
          }
  
      }