code: public Object get(final String key) {
          int i = _getInt(key);
          if (i < 0) {
              return null;
          }
          if (i >= size()) {
              return null;
          }
          return get(i);
      }
docs: Gets a value at an index. For interface compatibility.  Must be passed a String that is parsable to an int.
  
  @param key the index
  @return the value, if found, or null
  @throws IllegalArgumentException if {@code key} cannot be parsed into an {@code int}