code: public Errors add(Errors otherErrors) {
      if (otherErrors != null) {
        fieldErrors.putAll(otherErrors.fieldErrors);
        generalErrors.addAll(otherErrors.generalErrors);
      }
      return this;
    }
docs: Add all of {@code otherErrors} field and general errors to this object
  
  @param otherErrors can be null
  @return this