docs: @Size(2)
      @NonNull
      static String[] separateDateStringParts(@NonNull @Size(max = 4) String expiryInput) {
          String[] parts = new String[2];
          if (expiryInput.length() >= 2) {
              parts[0] = expiryInput.substring(0, 2);
              parts[1] = expiryInput.substring(2);
          } else {
              parts[0] = expiryInput;
              parts[1] = "";
          }
          return parts;
      }