base is undefined for cpp.libFlags in DynamicLibrary

Here is minimal qbs that show this error:

DynamicLibrary  {
    name: "lib"
    Depends { name: "cpp" }
    cpp.libFlags: base.concat([])
}

It gives error: "TypeError: Result of expression 'base'[undefined] is not an object".

But same construction works well for StaticLibrary