protected final Object get0(int n) {
    try {
      Object result = arr[n];

      if (result == null) {
        throw new NullPointerException("unset: " + n);
      }

      return result;
    } catch (ArrayIndexOutOfBoundsException ex) {
      // Translate the exception.
      return throwIndex(n);
    }
  }
Gets the indicated element. It is an error to call this with the index for an element which was
never set; if you do that, this will throw {@code NullPointerException}. This method is
protected so that subclasses may offer a safe type-checked public interface to their clients.

@param n {@code >= 0, < size();} which element
@return {@code non-null;} the indicated element
android/android_framework/dex-maker/src/main/java/com/android/dx/util/FixedSizeList.java