static boolean existsCheck(AttributeValue a, AttributeValue b, boolean caseInsensitive) {
        String bString = b.toString();
        return (a.isPresent() && bString.equals("true"))
                || (!a.isPresent() && b.toString().equals("false"));
    }
Compares the given attribute values by flattening each side of the
comparison, and comparing each value.

<p>This method is necessary in order to support matching on projections
using projection semantics.

@param singleComparison Comparison to apply to each element.
@return Returns the created comparator.
smithy-model/src/main/java/software/amazon/smithy/model/selector/AttributeComparator.java