public String getDeprecatedDescription(ShapeType shapeType) {
        StringBuilder builder = new StringBuilder("This ");
        builder.append(shapeType == ShapeType.OPERATION ? "operation" : "shape").append(" is deprecated");
        if (since != null) {
            builder.append(" since ").append(since);
        }
        if (message != null) {
            builder.append(": ").append(message);
        } else {
            builder.append(".");
        }
        return builder.toString();
    }
Gets the deprecation message value.

@return returns the optional deprecation message value.
smithy-model/src/main/java/software/amazon/smithy/model/traits/DeprecatedTrait.java