public TypeBearer peek(int n) {
    if (n < 0) {
      throw new IllegalArgumentException("n < 0");
    }

    if (n >= stackPtr) {
      return throwSimException("underflow");
    }

    return stack[stackPtr - n - 1];
  }
Peeks at the {@code n}th element down from the top of the stack. {@code n == 0} means to peek
at the top of the stack. Note that this will return {@code null} if the indicated element is
the deeper half of a category-2 value.

@param n {@code >= 0;} which element to peek at
@return {@code null-ok;} the type of value stored at that element
@throws SimException thrown if {@code n >= size()}
android/android_framework/dex-maker/src/main/java/com/android/dx/cf/code/ExecutionStack.java