code: private <T extends NamedDescriptor> T getOrCreateNamedDescriptor(Class<T> type, String name, Map<String, T> descriptors, Store store) {
          T descriptor = descriptors.get(name);
          if (descriptor == null) {
              descriptor = store.create(type);
              descriptor.setName(name);
              descriptors.put(name, descriptor);
          }
          return descriptor;
      }
docs: Get or create a named descriptor.
  
  @param type
  The descriptor type.
  @param name
  The name.
  @param descriptors
  The map of known named descriptors.
  @param store
  The store.
  @return The servlet descriptor.