@Override
    public Map<String, ShapeModel> process(Map<String, OperationModel> currentOperations,
                                           Map<String, ShapeModel> currentShapes) {
        // For backward compatibility we have to use both the checks, earlier the check was to only use
        // ModeledOutputShapeNames parameter.
        if (customizationConfig.useModeledOutputShapeNames() || customizationConfig.useModeledInputShapeNames()) {
            return currentShapes;
        } else {
            return addEmptyInputShapes(currentOperations);
        }
    }
This class adds empty input shapes to those operations which doesn't accept any input params. It
also creates a shape model for the shape with no members in it.
aws-java-sdk-code-generator/src/main/java/com/amazonaws/codegen/AddEmptyInputShape.java