public @Nls @Nullable String validateInput() {
    if (myUseDateAfterFilter.isSelected() && myDateAfter.getDate() == null) {
      return VcsBundle.message("error.date.after.must.be.a.valid.date");
    }
    if (myUseDateBeforeFilter.isSelected() && myDateBefore.getDate() == null) {
      return VcsBundle.message("error.date.before.must.be.a.valid.date");
    }
    return null;
  }
public @Nls @Nullable String validateInput()