code: public final DataHasher addData(DataHash dataHash) {
          Util.notNull(dataHash, "DataHash");
          return addData(dataHash.getImprint());
      }
docs: Adds {@link DataHash#getImprint()} to the digest.
  
  @param dataHash input digest.
  
  @return The same {@link DataHasher} object for chaining calls.
  
  @throws NullPointerException when input value is null.