code: Builder toBuilder() {
      Builder builder =
          builder()
              .setId(getId())
              .setIsHidden(isHidden())
              .setParts(getParts())
              .addAllSourceLocations(getSourceLocations())
              .setIsPlrselMsg(isPlrselMsg());
      if (getLocaleString() != null) {
        builder.setLocaleString(getLocaleString());
      }
      if (getMeaning() != null) {
        builder.setMeaning(getMeaning());
      }
      if (getDesc() != null) {
        builder.setDesc(getDesc());
      }
      if (getAltId() != -1) {
        builder.setAltId(getAltId());
      }
      if (getContentType() != null) {
        builder.setContentType(getContentType());
      }
      return builder;
    }
docs: Creates a new {@link Builder} based on the current instance.