private static void addTag(Javadoc doc, JavadocTag tag) {
		if (!hasTagAlready(
            requireNonNull(doc), 
            requireNonNull(tag)
        )) {
			doc.add(tag);
		}
	}
Add a javadoc tag to the specified documentation block. If the tag is
already defined, this will have no effect.

@param doc  the documentation block
@param tag  the tag to add
common-parent/codegen/src/main/java/com/speedment/common/codegen/controller/AutoJavadoc.java