code: public Trie2Writable set(int c, int value) {
          if (c<0 || c>0x10ffff) {
              throw new IllegalArgumentException("Invalid code point.");
          }
          set(c, true, value);
          fHash = 0;
          return this;
      }
docs: Set a value for a code point.
  
  @param c the code point
  @param value the value