@SuppressWarnings("unchecked")
        public T putProperty(String key, Object value) {
            properties.get().put(key, value);
            return (T) this;
        }
Sets a specific custom property.

@param key Key to set.
@param value Value to set.
@return Returns the builder.
smithy-codegen-core/src/main/java/software/amazon/smithy/codegen/core/TypedPropertiesBag.java