docs: private int getNextEmptyPosition(){
          int counter;
          for (counter = 0; counter < entries.length; counter++) {
              Entry e = entries[counter];
              if (e.isEmpty()) {
                  break;
              }
          }
  
          if (counter == entries.length) {
              throw new RuntimeException("Entry added to a node which is already full.");
          }
  
          return counter;
      }