code: private static void verifyId(final EntityMetadata entityMetadata) {
          if (!entityMetadata.hasIdProperty()) {
              throw new RepositoryMappingException("No field annotated with @Id present.");
          }
  
          if (entityMetadata.idProperty().type() != String.class) {
              throw new RepositoryMappingException("The @Id Field needs to be of type String.");
          }
      }
docs: Helper method to check that the ID field is present and is of the desired types.
  
  @param entityMetadata the entity metadata.