Error when generating iOS codesign entitlements: cannot read property 'bundle' of undefined

When building our iOS app with 2.5.0 we get the following error:

ERROR: cannot read property 'bundle' of undefined
    in /usr/local/Cellar/qbs/2.5.0/share/qbs/modules/codesign/codesign.js:571

Apparently the 'product' argument of the function 'generateAppleEntitlementsCommands' in the js file mentioned above is undefined when it is called.

Looking into "apple/codesign.qbs" the invocation is as follows as the prepare script of the rule:

Rule {
    ...
    prepare: CodeSign.generateAppleEntitlementsCommands(CodeSign, arguments)
}

I don't quite understand this. Why is it called with 'CodeSign' as the first parameter? And does 'arguments' have any special significance here?
Because aside from being moved into a Group item this rule hasn't changed from when it used to work.

For the time being I fixed it by simply calling the function inside of the prepare script and returning the result:

prepare: {
    return CodeSign.generateAppleEntitlementsCommands(project, product, inputs, outputs, input, output, explicitlyDependsOn);
}