private static String[] mergeArrays(@NotNull String[] a1, @NotNull String[] a2) {
    if (a1.length == 0) return a2;
    if (a2.length == 0) return a1;
    String[] result = new String[a1.length + a2.length];
    System.arraycopy(a1, 0, result, 0, a1.length);
    System.arraycopy(a2, 0, result, a1.length, a2.length);
    return result;
  }
private static String[] mergeArrays(@NotNull String[] a1, @NotNull String[] a2)