@Override
    public <T> T accept(ExpressionVisitor<T> visitor) {
        return visitor.visitIndex(this);
    }
Gets a specific element by zero-based index.

<p>Use a negative index to get an element from the end of the array
(e.g., -1 is used to get the last element of the array). If an
array element does not exist, a {@code null} value is returned.

@see <a href="https://jmespath.org/specification.html#index-expressions">Index Expressions</a>
smithy-jmespath/src/main/java/software/amazon/smithy/jmespath/ast/IndexExpression.java