yield error if a property is bound but not defined

Product {
    narf: "zort"
    // ERROR: Unknown property "narf" at location...

    bla.narf: "zort"
    // ERROR: Unknown property "bla" at location...

    Depends { name: "cpp" }
    cpp.knolf: "gnampf"
    // ERROR: Unknown property "knolf" at location...
}