enumeration type in key of list error

Generation of java code from this yang works:

typedef permission-type {
type enumeration

{ enum permit; enum deny; }

}

container access-control-services {
list access-control-service {
key "permission";

leaf permission

{ type permission-type; }

}
}

-------------------------------------------------------------
but generation from this has error

container access-control-services {
list access-control-service {
key "permission";

leaf permission {
type enumeration

{ enum permit; enum deny; }

}
}
}

[ERROR] /PathToGeneratedClass/AccessControlServiceBuilder.java:[75,54] incompatible types
required: packageName.AccessControlService.Permission
found: java.lang.Enum