public Optional<ShapeId> getUntagResourceOperation(ToShapeId serviceOrResourceId) {
        return Optional.ofNullable(shapeToUntagOperation.get(serviceOrResourceId.toShapeId()));
    }
Gets the ShapeID of the UntagResource operation on the shape if one is found meeting the criteria.
If a resource ID is passed in, it will return the qualifiying service wide TagResource operation ID rather than
the operation ID specified by the tagApi property.

@param serviceOrResourceId ShapeID of the service shape to retrieve the qualifying UntagResource operation for.
@return The ShapeID of a qualifying UntagResource operation if one is found. Returns an empty optional
  otherwise.
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/tagging/AwsTagIndex.java