private OperationShape.Builder transformInput(Set<ShapeId> removed, OperationShape operation) {
        if (removed.contains(operation.getInputShape())) {
            OperationShape.Builder builder = operation.toBuilder();
            builder.input(null);
            return builder;
        }
        return null;
    }
Removes references to removed structures from operation
input, output, and errors.
smithy-model/src/main/java/software/amazon/smithy/model/transform/plugins/CleanOperationStructures.java