docs: private Map<Character, DictSegment> getChildrenMap() {
          if (this.childrenMap == null) {
              synchronized (this) {
                  if (this.childrenMap == null) {
                      this.childrenMap = new HashMap<Character, DictSegment>(ARRAY_LENGTH_LIMIT * 2, 0.8f);
                  }
              }
          }
          return this.childrenMap;
      }