@Override
    public void returnAttributesValidation(ReturnAttribute[] returnAttributes) throws AnnotationValidationException {

        if (returnAttributes != null && returnAttributes.length > 0) {
            //Throw error for other classes as only in the classes extending
            //StreamProcessor or StreamFunctionProcessor allowed to have more than one ReturnAttribute.
            throw new AnnotationValidationException(MessageFormat.format("The @Extension -> @ReturnAttribute " +
                    "cannot be annotated in class {0}.", extensionClassFullName));
        }
    }
This processor will extend the validation rules for validate Distribution Strategy specific annotation contents.
modules/siddhi-annotations/src/main/java/io/siddhi/annotation/processor/DistributionStrategyValidationAnnotationProcessor.java