An open module doesn't declare any exports and instead, all packages are unqualifiedly exported.
In the jlr.Module implementation the isExported(-Private) methods return true when the module is open. There is no need to keep any data structures for exports. Also, methods like addExports are no-ops with open modules.
For now, the implementation special cases the instantiatation of open modules so that the VM is called to export each package. Instead, we should use the JVM_DefineModule "open" flag to equate to exporting all packages unqualifiedly.