The "base.concat" pattern does not work for product types

import qbs
import qbs.TextFile

CppApplication {
    type: base.concat("mytype") // Does not work
    // type: ["application", "mytype"] // Works
    files: "main.cpp"
    Transformer {
        Artifact {
            filePath: "mytype.txt"
            fileTags: "mytype"
        }
        prepare: {
            var cmd = new JavaScriptCommand();
            cmd.description = "Generating file";
            cmd.sourceCode = function() {
                var f = new TextFile(output.filePath, TextFile.WriteOnly);
                f.writeLine("Huhu!");
                f.close();
            }
            return cmd;
        }
    }
}