public static @Nullable @Nls String combineAccessibleStrings(@Nullable @Nls String s1, @NotNull @NlsSafe String separator, @Nullable @Nls String s2) {
    if (StringUtil.isEmpty(s1))
      return s2;
    if (StringUtil.isEmpty(s2))
      return s1;
    return s1 + separator + s2;
  }
public static @Nullable @Nls String combineAccessibleStrings(@Nullable @Nls String s1, @NotNull @NlsSafe String separator, @Nullable @Nls String s2)